Lab: Sensitising, Printing and Toning an Albumen Print

Purpose

To turn a coated sheet into a mounted photograph, and to do it inside the limits a protein layer imposes on every bath it meets.

One number governs this session more than any other. The silver bath is doing three jobs at once — making silver chloride, leaving the excess of free silver nitrate that printing out depends on, and coagulating the binder so it does not wash off the paper — and the third job is the one no other sheet in Parts XXI to XXV asks of a sensitiser. Get the float wrong and you do not get a weak print; you get a tray of dissolved egg white and a sheet of blank paper.

Learning objectives

By the end of this session you should be able to:

• State the three jobs the silver bath does on an albumenised sheet, and explain why a strong bath needs a longer float rather than a shorter one.
• Float, time, draw and dry a sensitised sheet under safelight without trapping air, wetting the back or over-drying it.
• Say what the keeping time of a sensitised sheet is, what extends it, and what that extension costs.
• Explain what ammonia fuming did, why it worked, and why this course teaches it and gives no procedure.
• Judge a printing-out exposure by inspection, and say what bronzing tells you.
• Run the first wash, gold toner, two-bath alkaline fixer, washing aid and final wash with the albumen-specific limit on each, and say what each limit protects.
• Mount a print that would otherwise curl into a tube.
• Record and measure enough to fill the third row of the process comparison atlas.

Prerequisites

Lab: preparing and coating albumen paper, because this session starts with your own coated sheets and your own record of how they were made.

Lab: salting and sensitising a sheet of paper and Lab: printing, toning, fixing and washing a salt print from Part XXII. This page assumes you have already floated a sheet on silver nitrate, printed one out under a negative, judged a gold toner by eye and taken a printed-out image through fixing and washing. It gives the differences, not the sequence.

Gold toning and the permanence of printed-out silver, which owns the mechanism. Nothing about why gold protects a printed-out image is repeated here.

The silver nitrate handling SOP and the silver-bearing waste SOP, read before the session and not during it.

Safety classification

Level B, and silver nitrate sets it. The rubric’s Level B criteria that apply are: handling of a concentrated reagent that the rubric names explicitly; a procedure whose failure mode is “a splash, a burn or a spill of something corrosive rather than merely a spoiled negative”; and an ultraviolet exposure. Silver nitrate’s aggregated classification is Danger, with H272 may intensify fire, H290 may be corrosive to metals, H314 causes severe skin burns and eye damage, H318 causes serious eye damage, H360D may damage the unborn child, and H400/H410 very toxic to aquatic life with long-lasting effects.

!A correction to a common expectation about the concentration

This part is often described as using a higher silver concentration than plain salted paper. On Reilly’s own figures that is not so, and it is worth being exact because the sentence gets repeated.

His recommendation for most salted papers is a chloride content of about 2 to 2.5 per cent with the silver bath at 10 to 12 per cent. His recommendation for modern albumen practice is a chloride content of 1.5 per cent or above with a silver bath of 10 per cent or above. Same band. What differs is the float — two and a half to three minutes, and Reilly says that is adequate even for doubly albumenised paper — and why it differs, which is job three.

Two real routes do use more. Bostick & Sullivan’s kit supplies 15 per cent, and Hardwich’s 1864 bath, which the formulary carries, is 90 grains to the fluid ounce — 20.5 per cent w/v, nearly twice Reilly’s. If you follow either of those, the level does not change but the arithmetic in Estimated consumables cost does. This lab uses Reilly’s, which is what the course recommends for modern work.

A declared higher-level step, and it is the one this page does not perform. Ammonia fuming would be Level C and is excluded. The chemistry and the history are taught below under What is happening chemically; no procedure is given anywhere on this page. The grounds are in the Hazards table and they are numerical rather than rhetorical.

⚠What is not a hazard here, and why

The exposure is not a chemical hazard, and the ultraviolet is not an incidental one. Nothing is mixed, heated or decanted while the frame is out. What is present is an ultraviolet source, and that is a skin and eye exposure whether it is a lamp or the sky. The controls are Part XVI’s and they run enclosure and interlock before eyewear.

The gold toner is not a poisoning risk at this dilution, and it is still not casual. Chloroauric acid — which is what is sold as “gold chloride” — carries H314, H317 and H318 as the solid and the stock solution. The working bath is 0.4 to 0.5 g per litre. What survives that dilution is the sensitisation statement, H317, so gloves stay on; what does not is the corrosivity, and the course says so rather than repeating a solid’s classification over a tray of dilute liquid.

The plain thiosulfate fixer is the mildest thing on this bench. Sodium thiosulfate pentahydrate has no GHS classification at all: signal word None, no pictograms, no hazard statements. What makes a spent fixing bath a waste problem is the silver dissolved in it, not the thiosulfate — which is exactly why it goes to recovery rather than away.

And the albumen is no longer the mild material it was last session. The moment a coated sheet touches the silver bath it becomes a silver-bearing object, its rinse water becomes silver-bearing waste, and its trimmings become something you keep rather than bin. The level belongs to the operation, and this is the operation where it changes.

Hazards

What	The hazard	The control here
Silver nitrate, 10 to 12 per cent, in an open tray	Danger. H314, H318, H360D, H272, H290, H410. Reilly: “Silver nitrate can cause permanent, irreversible eye damage”, and sheets dripping silver solution “pose a special hazard to eyes”	Chemical splash goggles, not spectacles, from before the bottle is opened until the tray is emptied. Nitrile gloves, apron, covered bench, spill tray under the tray. Glass or new plastic vessels; no stainless steel, which Reilly rules out, and no metal utensils. Silver nitrate handling SOP and spill SOP
Repeated skin contact with silver nitrate	Staining that is permanent on surfaces and slow to fade on skin; and, on Reilly’s own account, prolonged absorption leading to argyria — irreversible staining of the conjunctivae, blood vessel walls, gums and mucous membranes — with “consequences more serious than staining of the tissues” also reported	Gloves are not optional and hands are washed immediately after any contact. Bostick & Sullivan’s blunter version: the solution “will leave a black stain on skin, clothing and almost any other surface. Removal of these stains can be very difficult!”
Chloroauric acid stock, 1 per cent	Danger; H314, H317 may cause an allergic skin reaction, H318, H373, H411. The stock is the hazard; the working bath is 0.4 to 0.5 g/L	Goggles and gloves for the stock. Gloves stay on for the working bath because H317 is a sensitisation statement and dilution does not remove it
Sodium thiocyanate or ammonium thiocyanate, where the thiocyanate toner is used	Danger; H302, H312, H332, H318, H412. And the incompatibility that governs the bench: a thiocyanate must never be acidified	The thiocyanate rule. The toner is never acidified, and no acid bath is present at this bench or in its waste bottle — no stop bath, no acid fixer, no vinegar, no “redding up” tray. See incompatibilities. If you want an acid-free session, use the borax toner instead
Ammonia solution, if fuming is attempted	HSE’s EH40: 25 ppm (18 mg/m³) over eight hours, 35 ppm (25 mg/m³) over fifteen minutes. Chemical Safety Card 0215 records that harmful air contamination “can be reached very quickly on evaporation of this substance at 20 °C”	Not performed. A dish of concentrated ammonia evaporating in a closed box is a deliberate vapour generator and controlling it means engineered extraction, which is Level C. No procedure is given
Ammonia near the silver bath, in any form	Reilly: “one clear danger in the use of ammonia in silver baths is the potential for the formation of fulminating silver, a highly explosive substance”	No ammonia bottle is in the room while the silver bath is open. See the ammoniacal silver quench SOP for what to do if the two have met
Ultraviolet, lamp or sunlight	Skin and eye exposure, with nothing to tell you it is happening	Part XVI’s controls: enclosure and interlock for a unit; the outdoor exposure SOP for the sky
Glass negatives under pressure	Reilly: a splinter of wood between the glass of the frame and the negative “can fracture the negative once pressure is applied”; and a cold frame put out in sunlight can crack a plate by unequal expansion	Felt pads, clean glass, a frame intended for plates, and a 1 mil polyester spacer between negative and paper
Every solution in the session	All silver-bearing, including the first wash: Reilly puts most of the recoverable silver “in the first and second changes of wash water”	Collected, labelled and dated under the silver-bearing waste SOP

Required PPE

Chemical splash goggles, for the whole of the wet work. Not safety spectacles. This is the single control both sources put first and Reilly puts it in capitals twice: “Always wear eye protection when compounding or handling silver nitrate solutions!” and “The most important precaution, however, is to wear eye protection; sheets dripping silver solution pose a special hazard to eyes.”

Nitrile gloves, changed when they get silver on them, and hands washed immediately after any contact. Reilly’s instruction is “tightly fitting” gloves for sensitising, for the good reason that a loose glove is what dips into the tray. See glove selection.

An apron and closed shoes, which is Bostick & Sullivan’s list as well as the rubric’s.

A covered bench and a spill tray. A spill nobody notices is a contamination source for every session afterwards, and the stain is the least of it.

Eyewash within reach, which is what Level B means by the phrase — see first aid and the eyewash SOP.

And a light discipline that is PPE for the paper rather than for you: every operation from the silver tray onwards is a safelight operation.

Ventilation

Ventilation is a control here for a hazard that is largely absent, and saying so precisely is more useful than a generic instruction. Nothing in this session is heated, nothing is a volatile solvent, and neither silver nitrate nor thiosulfate nor a dilute gold bath produces a vapour at room temperature. The Level B requirement of “local extraction or work near an open window with a fan” is met by an openable window or an extractor running, for two reasons.

A printing session generates aerosol when trays are agitated, and an aerosol of a corrosive solution is a different exposure from a liquid sitting in a dish.

And the one operation that would need real extraction is the one this page refuses to do. Ammonia fuming needs engineered extraction; that is why it is not here. Ventilation is not what would make fuming acceptable at home — the absence of fuming is what makes this room’s ventilation adequate. If you dry sensitised sheets with warm air, that air leaves the room rather than recirculating over the bench.

Materials

Material	Quantity for the worked session	Note
Coated albumen paper from the last session	6 to 10 sheets, 10 × 12 in	Conditioned overnight somewhere damp. Reilly: sheets “must not be excessively dry at the time of sensitization, because if too dry, they will not properly absorb the silver nitrate solution”
Your standard negative	1	The same negative as your cyanotype and your salt print, or the atlas row is worthless. Albumen wants a shorter density range than plain salted paper and a much longer one than an enlarging paper
1 mil polyester sheet	1 piece, larger than the negative	Reilly’s spacer. It protects the negative from silver transfer “without sacrificing sharpness”
Felt pads for the printing frame	As the frame takes	To distribute pressure, and lying flat when the frame is re-closed
Distilled or deionised water	2 to 3 L	For the silver bath and the toner. Reilly: tap water precipitates silver chloride and carbonate in the bath and “robs the bath of strength”
Blotting paper, acid-free	Several sheets	For blotting runoff during drying and for blotting the finished print
Fibreglass or plastic drying screen	1	Prints air-dry face up
Mount board and mounting materials	Per print	See Storage

Chemicals

Chemical	Quantity	Form
Silver nitrate	120 g per litre of bath	Solid, dissolved in distilled water to make a 12 per cent w/v bath
Kaolin	15 g per litre of bath	Powder, shaken into the stored bath after each session. The encyclopaedia has no page for it; it is a china clay used here as an adsorbent and it takes no part in any reaction
Citric acid	Optional; 1 to 5 per cent of the bath	Solid. Only if the sheet has to keep more than a day, and read the cost first
Chloroauric acid (“gold chloride”)	0.4 to 0.5 g per litre of working toner	1 per cent stock solution in distilled water
Borax	10 g per litre	For the borax toner
Sodium thiocyanate	15 to 20 g per litre	For the thiocyanate toner, if that is the one chosen
Sodium thiosulfate pentahydrate	150 g per litre, in each of two baths	The 15 per cent fixer
Sodium carbonate	2 g per litre of fixer	The alkalinity that promotes fixation and helps prevent blistering
Sodium sulfite	10 g per litre	The 1 per cent washing aid, used once and discarded

Every quantity above is on its formulary page with its provenance and the function of each ingredient: the albumen sensitiser, the gold-borax and gold-thiocyanate toners, Reilly’s alkaline fixing bath and the hypo clearing agent. Nothing is repeated here that the formulary carries, and where this page gives a number it is because the number is a limit rather than a recipe.

Equipment

• A glass tray for the silver bath, slightly larger than the sheet. Reilly: “Ideally, the tray, and all containers used for the silver solution, should be made of glass. A stainless steel tray is not recommended. If a plastic tray has to be used, it should be new, because plastic tends to hold on to chemicals.”
• A glass rod, “useful for bursting stubborn bubbles and for lifting the corners of the sheets”. Drawing the sheet over a rod as it comes off, which old manuals recommend, “is unnecessary if the sheets are slowly peeled from the surface”.
• A three-minute timer. Reilly suggests an egg timer, which is either a joke or the least surprising sentence in the book.
• Four more trays, marked and never swapped: toner, fixer 1, fixer 2, washing aid. Plus a washing tray or a print washer.
• A brown storage bottle for the silver bath, with the kaolin living in it.
• A split-back contact printing frame with felt pads, and a UV unit or the sky.
• A low-wattage white incandescent lamp, away from the bench, for judging exposure and toning. Not a yellow one, and the reason is under Procedure.
• A safelight — red, and it can be bright.
• A thermometer, because 21 °C across every bath is a real requirement here rather than a convention.
• A densitometer (Part XV) and a step tablet, for the atlas row.
• A loupe, for the finished print.
• Nothing metal anywhere near the silver: no metal-ferruled brush, no steel tongs, no steel tray.

Estimated cost

The band is £££, and it is the only page in this part that earns it. The reason is one substance. The planner carries what the price file can price; the section below says how much of this page it cannot.

Estimated consumables cost

Every price with a number is the planner’s own dated UK figure and every quantity comes from the Materials and Chemicals sections above. The worked session is six 10 × 12 in sheets sensitised, printed, toned, fixed and washed, from a litre of 12 per cent bath that already exists.

Consumed	This session	Sourced price	Cost this session
Nitrile gloves	4 pairs	£6.64 to £14.99 per box of 50 to 100	£0.53 to £1.20
Silver nitrate carried off in the sheets	About 36 g — see the arithmetic below	£59.95 per 25 g, or £112.90 per 10 g: £2.40 or £11.29 per gram	£86 to £406
Sodium carbonate, anhydrous	4 g, into two litres of fixer	£7.20 per 500 g	£0.06
Sodium sulfite, anhydrous	10 g, into a litre of washing aid	£13.68 to £19.98 per 1 kg	£0.14 to £0.20
Sodium thiosulfate pentahydrate	300 g, into two litres of 15 per cent fixer	£14.70 per 1 kg of the raw salt, checked 7 September 2026	£4.41
Chloroauric acid	0.4 to 0.5 g in a litre of one-use toner	Not priced, and the gap the file records for it names this bath’s own 0.4 to 0.5 g/L as the albumen figure	—
Borax, or sodium thiocyanate	10 g, or 15 to 20 g	Borax £9.98 per 200 g; the thiocyanate is not priced, and the file’s gap for the three thiocyanates names this toner as one of the three places they are wanted	£0.50, or —
Kaolin	About 15 g, into the storage bottle	Not priced	—
Distilled water	2 to 3 L	Not priced	—
Coated albumen paper	6 sheets	Not priced — see the coating lab, where every input to it is unpriced too	—
Mount board, starch paste, hinges	Per print mounted	Not priced	—

The priced subtotal is dominated by one row and it is not close. Gloves, carbonate, sulfite, borax and the hypo together come to about £5.60 to £6.40; the silver comes to somewhere between £86 and £406. Everything else has no sourced price, so the total is a floor and not a total — but it is a floor that already tells you the whole economics of the process. Equipment is not in the table: a tray is not consumed, a printing frame is not consumed, and a densitometer is certainly not consumed.

🧮Where the 36 g comes from, and how much of it you get back

Reilly’s replenishment example is the only per-session figure in the corpus. “If the original strength and volume were 1 liter of 12% silver solution and after a printing session only 850 ml remained, replenish with 150 ml of 24% silver solution.”

150 mL × 240 g/L = 36 g

Silver nitrate to restore the bath

That 36 g is what the sheets carried away, and at the two dated UK listings’ per-gram figures of £2.40 and £11.29 it is £86 to £406 of silver. The size of that session is not stated, so the per-sheet figure below chains it to a second Reilly statement from a different paragraph — that a 12 per cent bath serves “perhaps two or three batches — say a total of 30 11 x 14 prints” before the strength needs checking. Combining the two is the course’s inference, not Reilly’s statement.

36 g ÷ 30 = 1.2 g of silver nitrate per 11 × 14 in sheet

Per sheet, if the session was 30 prints

which is £2.90 to £13.50 of silver in every sheet you float, before you have exposed it. Scale that to your own sheet size by area: an 11 × 14 in sheet is 9.94 dm², so it is about 0.12 g per square decimetre.

And most of it does not end up in the picture. Reilly: “Only about 6-8 % of the silver initially present in a sheet of sensitized paper is utilized to form the image; the rest is washed or fixed away in processing.” So of the £2.90 to £13.50, something like 20p to £1 becomes photograph and the rest goes into the wash water and the fixer — which is why every one of those solutions is collected, and why a nineteenth-century gallery recovered about 60 per cent of the silver it consumed. Whether recovery pays you is a separate question, and Reilly’s answer for a small worker is that minimum charges and shipping usually make it “not worth the trouble”. That is an economic judgement and not a disposal one; the solutions are still collected. See silver recovery and the responsible darkroom.

Waste streams

Stream	What is in it	Where it goes
Spent silver bath, and the kaolin sludge under it	Silver nitrate, ammonium or sodium nitrate, dissolved albumen, reduced metallic silver	Silver-bearing. Bottled, labelled, dated. The bath is normally kept and replenished rather than discarded, so this stream is small and occasional
The first wash	Free silver nitrate washed out of the sheet, and the cloudy silver chloride it makes with the ions in tap water	Silver-bearing, and it is the biggest single silver stream on this page. Reilly: most of the recoverable silver “is found in the first and second changes of wash water”. Collect it
Spent gold toner	Gold, silver chloride formed by the substitution, and the toner’s own borax or thiocyanate	Collected separately. It carries a precious metal and, if thiocyanate, a substance that must never meet acid
Spent fixer, both baths	Silver-thiosulfate complexes, thiosulfate, carbonate	Silver-bearing, to recovery. The thiosulfate itself has no GHS classification; the silver is the reason this bottle exists
Spent washing aid	Sodium sulfite carrying displaced thiosulfate	Modest, and collected with the fixer stream
Final wash water	Traces	The general rinse stream, and the first two changes of it go in the silver bottle rather than away
Print trimmings and spoiled prints	Paper carrying image silver and gold	Kept. Reilly notes trimmings and spoiled prints are a recoverable source, historically by burning and recovering from the ashes

One rule that has no exception on this page. No acid enters any of these bottles, because the gold toner bottle may contain a thiocyanate.

Alternative route

No darkroom. You do not need one: this session needs subdued light, not darkness. Bostick & Sullivan specify a safelight, a red compact fluorescent bulb or red LEDs and add that “the red lights used can be very bright and will not interfere in the processing”. Reilly adds one requirement to that: a low-wattage white incandescent lamp for judging exposure and toning, because “yellow light does not allow the separation of tones in the middletone and shadow areas to be clearly seen”. A room with the window blocked, a red lamp on the bench and a dim white lamp across the room meets the specification, and so does a bathroom at night.

What has no substitute is a sink with running water. Four of the baths here are running-water operations and the last needs the whole volume changed every five minutes; a tray and a jug will do that for one or two prints and not for six.

No ultraviolet unit. Sunlight, and this is one of the processes it suits. Reilly’s average exposure for albumen paper in direct sunlight is 5 to 10 minutes; in shade — meaning facing open sky and not in the sun — “anywhere from ½ hour to several days”. Two of his limits are worth planning around: sensitivity is “considerably lowered when the temperature dips below 5 °C, so printing outside in winter is practically impossible”, and a cold frame taken into sunlight can give “a ‘doubled’ image all around the outside edges of the image area while the center of the print remains sharp and crisp” because paper and negative expand unequally. Use the daylight exposure record SOP and record conditions rather than a dose. Never open the frame to inspect in sunlight or open shade; Reilly says bring it inside, and Bostick & Sullivan say the same and add a limit — inspection under normal room light for no more than ten seconds at a time.

No silver nitrate, or no budget for it. There is no route to a printed-out silver image without it, but a smaller tray takes a smaller bath, because the volume is set by the tray rather than by the sheet. Bostick & Sullivan’s kit exists for this reason: their 15 per cent litre is a fixed, known quantity you can budget once.

No way to run the wet work at all. Then this page is reading, and the two arguments survive reading: why a strong bath needs a longer float, and why every bath after the frame is limited by a protein rather than by a silver chemistry. What cannot be substituted is the judgement, because printing and toning by inspection are skills of the eye.

Preparation

The night before. Condition the coated sheets somewhere damp — Reilly says a basement, and a closed box with an open dish of water in it does the same job. This makes them absorb the sensitiser evenly and makes them supple enough to handle. Bring the negative, the frame and the polyester spacer together and check the glass is clean.

Mix the silver bath at least a day ahead if you can, in distilled or deionised water: with tap water “the silver nitrate will react with chlorine and ‘hard water ions’ such as carbonates”, giving a cloudy precipitate that “robs the bath of strength and makes sensitizing difficult.” Add the kaolin, shake, settle overnight, and decant off the clay before use. A bath that has already silvered some sheets behaves better than a fresh one, for the reason under What is happening chemically.

Make the fixer fresh on the day. Reilly is explicit: two baths, “both of which must be freshly made up the day on which they will be used.”

Bring everything to 21 °C — Reilly’s “about 70 °F (21 °C)” for all solutions including the fixer — and check it with a thermometer rather than by feel. This is the single most-skipped instruction on the page and it is what stops blisters.

Set the trays out in order and mark them, and put the acid bottle away in another room. It is not needed here, and if you are using a thiocyanate toner it must not be in the building’s darkroom at all.

Procedure

Sensitising

1. Under safelight from here on. Bostick & Sullivan draw the boundary precisely and it is easy to get wrong in both directions: the silver nitrate solution itself is not light-sensitive, but “it will become light sensitive when it comes in contact with any organic substance” — which on this bench means the moment it touches the paper.

2. Filter the bath and pour it into the glass tray. Filter it whenever a surface scum has appeared, which Reilly says shows up “as a metallic marbled sheen on exposed prints” if you do not.

3. Clear the surface. Hardwich’s method is a folded strip of blotting paper cut to the exact breadth of the dish and drawn lightly across before each sheet; Reilly blows gently on the bubbles to burst them or move them to the side.

4. Float the sheet, centre first, and check for trapped air. Bubbles here are not a cosmetic problem: “bubbles prevent sensitization where they occur, and will cause white circles on the face of the finished print” — paper-white, with hard definite edges, which is how you tell them from the light-brown-stained circles a bubble in the coating bath leaves.

5. Start the clock when the sheet lies flat and every bubble is gone. Float for 2½ to 3 minutes. Reilly states that this “insures adequate sensitization of even doubly albumenized paper”. Do not agitate, do not rock the tray, do not extend the float because the sheet looks pale.

6. Draw it off slowly, one corner peeled up and away. “When the sheet has been properly lifted, hardly a drop will leave the sheet while it is held in the air over the tray to drain.” No silver reaches the back of the sheet: patches of uneven density are the result if it does. Bostick & Sullivan give a drip-rate end point for the drain — hold it until there is at least twenty seconds between drops.

7. Hang by two corners of the long edge, on a line inclined 5 to 7 degrees, and blot the low corner. Reilly: blotting the drops that form there “is essential to speedy drying and even sensitization”.

8. Dry, but do not over-dry. Mild heat may be used to accelerate it. Reilly’s limit is a photographic one rather than a safety one: “albumen paper will become brittle if excessively dry”, and a paper that is too dry at the time of printing gives flat, weak prints.

The float: the draw that works, and three that do not

1. 1Correct — flat, no air, timed from the moment the last bubble went, 2½ to 3 minutes at about 21 °C, peeled off slowly at a shallow angle
2. 2Float too long, or agitated, or warm — the albumen dissolves before the silver has coagulated it. The layer goes into the tray and the tray is now contaminated
3. 3Lifted too fast — a flood of runoff gives uneven sensitisation, and silver on the back gives patches of uneven density
4. 4Bubbles left underneath — no sensitising where they sat: paper-white circles with hard edges on the finished print
5. 5The coupling — strong bath, faster coagulation, slower permeation, longer float. Weak bath, faster permeation, and a race against dissolution

The failure modes are Reilly's and the drawing arranges them; the panels are schematic and not to scale.

Printing

9. Load the frame under safelight. Clean glass, felt pads lying flat, the 1 mil polyester spacer between negative and paper. Reilly’s warning about a splinter of wood fracturing a glass negative under pressure is worth a look before you close the frame on anything valuable.

10. Expose, and inspect. Under a UV unit, or in sunlight at 5 to 10 minutes as a starting point. Open half the split back, keep registration, and look. Bostick & Sullivan: inspect under normal room light for no more than ten seconds at a time, and never outdoors or in direct sunlight.

11. Print deep. Every printed-out image loses density in toning and fixing, so “in all cases the print should appear too dark … when leaving the printing frame.” Reilly’s starting figures: overprint about one and a half stops for albumen and two for salted papers, and double-coated albumen needs less than single-coated.

12. Read the bronzing. Watch the margins, which have no negative over them and reach maximum density first. “A guide to the point when maximum density has been attained is when the margins of the print begin to ‘bronze’, that is, take on a greenish luster. At this point so much metallic silver has been reduced in the light-sensitive layer that a kind of saturation point is reached and particles of silver migrate to the surface of the layer and form a coherent, shiny film.” Many old manuals say print until the shadows are just bronzed, and Reilly calls that correct advice for negatives that can be printed in full sunshine.

13. Keep exposed prints in the dark until every one is ready to process; they are still light-sensitive.

Processing

14. First wash. Running water, agitated, until the cloudy precipitate has gone from the wash water — and then a little more, but not past ten minutes in running water. Reilly’s reason: “excessive washing removes the last small traces of silver nitrate that are necessary for some toners to work properly.” See the callout below before you follow this, because a modern kit says the opposite.

15. Tone. Full strength for ordinary glossy albumen — 0.4 to 0.5 g of gold chloride per litre, four to five times the 0.1 to 0.2 g/L used for matte salted papers, “because albumen is less permeable and the silver particles are more protected”. Toner at 17 to 20 °C, constant agitation, prints kept uniformly wetted. Ten to fifteen minutes or longer is the target; Reilly’s reason for the leisurely pace is that “there is less chance of over-toning, and there is time to consider whether the prints are toned to the desired extent.”

16. Judge by transmitted light, under weak white incandescent light. Hold the print up. “When by transmitted light the last traces of warm color have disappeared from the print, the toning process is quite advanced, and the final color of the print is likely to be purple or purplish-black.” Stop before it looks at all bluish: over-toning substitutes too much gold for silver, and the print turns “an unpleasant slate blue color” and loses density.

17. Leave one print completely untoned and take it through fixing and drying with the others. Reilly recommends this for beginners, and without it you have no baseline for what toning did.

18. Wash five minutes in running water before fixing: a trace of fixer ruins a toning bath, so this wash protects the next batch as much as this one.

19. Fix in two baths of 15 per cent sodium thiosulfate, alkaline with 2 g of sodium carbonate per litre, both freshly made today. Four minutes in the first with constant agitation, drain at least five seconds, four minutes in the second. Reilly’s reason for two baths is chemical: some reaction products of silver chloride and thiosulfate are insoluble in water and would never wash out, but they are soluble in fresh thiosulfate.

20. Wash 2 to 4 minutes, then 1 per cent sodium sulfite for 3 to 4 minutes with constant agitation, used once and discarded.

21. Final wash, 30 minutes, the whole volume changing at least every five minutes, with hand agitation if the washer is a tray with a siphon. “Extremely heavy base stocks and very thick coatings of albumen may indicate that a longer wash time — 40 to 50 minutes — is required.”

22. Blot and dry face up on a fibreglass screen, or squeegee face-down on clean glass first.

The sequence, with the albumen-specific limit on each bath

1. 1First wash — running water, and stop at 10 minutesRemoves the bulk of the free silver nitrate. Reilly caps it because the last traces of silver nitrate are needed by some toners. The print reddens here, and that is swelling rather than chemistry. All of this water is silver-bearing
2. 2Gold toner — 0.4 to 0.5 g/L, 17 to 20 °C, 10 to 15 minutes, constant agitationFour to five times the strength a matte salted paper needs, because albumen is less permeable. Judged by transmitted light. Variations in coating thickness show here first, because thin areas tone faster and deeper
3. 3Wash — 5 minutesCarries no fixer into the toner and no toner into the fixer. A trace of fixer ruins a gold bath
4. 4Fixer 1 — 15 % thiosulfate, alkaline, 4 minutes2 g of sodium carbonate per litre. Alkalinity promotes fixation and helps prevent blistering of heavily albumenised sheets. Made up fresh today
5. 5Drain 5 seconds, then Fixer 2 — 4 minutesTwo baths because some reaction products are insoluble in water and soluble only in fresh thiosulfate. This is the step that decides whether the print survives a century
6. 6Wash 2 to 4 minutes, then 1 % sodium sulfite for 3 to 4 minutesThe washing aid displaces absorbed thiosulfate with more soluble ions. One use and discard; no more than 20 8 × 10 prints per litre
7. 7Final wash — 30 minutes, or 40 to 50 for thick coatings on heavy stockThe whole volume changed at least every five minutes. Reilly notes some image layers may begin to dissolve if washing is prolonged past what they need, so this is a limit in both directions
8. 8Blot, dry face up, flatten and mountColour and density come back on drying. Mount while slightly damp, because a dry sheet with a thick albumen layer will not lie flat

Every time and strength is Reilly's, on his figures for albumen specifically. The temperature that applies to all of them is about 21 °C, and the reason is blistering rather than reaction rate.

⁇How long the first wash should be: ten minutes, or thirty

The two sources this part relies on give opposite instructions, and both give a reason.

Reilly caps it. “Although the washing should be continued past the point where the wash water is free of the cloudy precipitate of silver chloride, do not allow the first wash to go on past 10 minutes in running water. Excessive washing removes the last small traces of silver nitrate that are necessary for some toners to work properly.”

Bostick & Sullivan extend it. “Wash the print for a minimum of 25 to 30 minutes”, with at least five complete changes of water, and their reason is the opposite risk: “Any extra silver nitrate left in the print will cause anomalies, such as brown spots and foxing, which will not be immediately visible, but can form on the print at any point in the future.”

Both are describing real failures. A toner starved of residual silver tones weakly and unevenly; a print left with free silver nitrate in it stains later. They differ because they are protecting different things and because they are not using the same toner. Reilly says so himself: with each of his gold baths “there will be slight differences in rate of toning, and with the thiocyanate toner a difference in the mechanism of toning” — and a thiocyanate bath, as its formulary page sets out, both plates gold onto the image and etches the image it is plating.

What the course uses, and why. Follow the source whose toner you are using. On Reilly’s borax or thiocyanate toners, wash until the milkiness has gone and stop before ten minutes. On the Bostick & Sullivan kit, follow the kit. And whichever you do, collect the water, because the disagreement is about how much silver leaves the print and not about where it goes: Reilly puts most of the recoverable silver of the whole process in the first and second changes of wash water.

What would settle it is a residual-silver test on prints washed both ways from the same batch, read against toning quality. It is listed under Further experiments, and nobody read for this course has published it.

Mounting

23. Trim, then mount while the print is slightly damp, or rewet and blot it. Period trimming was done against brass templates with a rotary blade, which is why so many albumen prints have curved or oval image edges and why their mounts have rounded corners; and mounting was followed by rolling or burnishing, which is where the gloss of a cabinet card comes from. Reilly’s reason for mounting damp is force: “the force exerted by a thick layer of albumen is quite enough, if a print has been incorrectly mounted, to tear the print in half.”

24. Starch paste if you paste at all, and never dry mounting. Conservators removing albumen prints from their mounts “agree that pure fresh starch has proven itself as the best choice for a mountant”; dry mounting “should never be used with albumen or salted paper prints, because of color shifts caused by heat, and the irreversibility of the process.”

25. Or do not mount at all. A polyester sleeve with a two-ply acid-free rag board, or a window mat of museum board — Reilly’s two current museum methods, both of which “form a safe environment for the print yet are not permanently attached to it.”

The reasoning behind all three, and the evidence about mount boards and adhesives that stands behind it, is the next page’s.

Expected observations

On the silver bath. It begins colourless and goes brown with use, then darker. This is not spoilage: albumen and size dissolve off every sheet, react with a little of the silver, and the silver is spontaneously reduced to finely divided metal, which is what colours the solution. A slightly discoloured bath is usable and a nearly black one is not; kaolin clears it. Bostick & Sullivan report the colour as red rather than brown and blame salt carried out of the albumen — an observation the corpus does not reconcile, and the course records both.

On the sensitised sheet, drying. It curls, and it begins to go faintly yellow if it sits — and that yellow is not dirt: “the yellow color is actually spontaneously reduced metallic silver in a very finely divided state.”

In the frame. The image appears and keeps deepening. The margins reach maximum density first and then bronze. Colour out of the frame runs from rich purple to dark brown, and Reilly’s remark is the one every printer repeats: the prints “are very beautiful as they come from the frame, and many writers on the albumen printing process have remarked that they wished the prints could be preserved in that state forever.”

In the first wash. Milky water — that is silver chloride precipitating as the free silver nitrate meets the ions in tap water — and a print that reddens. The reddening is the layer swelling, not a reaction.

In the toner. A slow shift towards lilac or purple, uneven at first if the coating is uneven, and prints in one batch will not tone at the same rate.

In the fixer. A dramatic loss of colour and density, and the purple disappears. This is expected and physical: fixing removes the silver chloride, which lowers the refractive index of the system and lets the silver particles pack together, so covering power falls and the colour shifts yellow.

On drying. It comes back. The print becomes darker and colder as the layer contracts. Bostick & Sullivan describe two to three hours in which “the shadow density will deepen to a warm, rich tone and the highlights will take on a red/pink color.”

And if something has gone wrong with the temperature or the pH, blisters — raised bubbles in the layer. Reilly: small ones sometimes disappear on drying, “but if they are large or break, then the prints are usually ruined.”

What is happening chemically

The three jobs of the silver bath, and why they fight

One: make the halide. The double replacement, with the cation as a spectator.

NH₄Cl + AgNO₃ → AgCl + NH₄NO₃

Silver chloride precipitated in place, inside the protein layer

Two: leave the excess. Printing out needs far more silver nitrate than the chloride can consume. Part XXII owns the mechanism; the short form is Vogel’s, in Reilly’s words: light dissociates silver chloride, the liberated chlorine unites with the excess silver nitrate to form new silver chloride, light breaks that down in turn, “and the cycle begins again”.

Three: coagulate the binder. Albumen is one of the proteins that metal salts precipitate, and silver nitrate does it in this tray. Reilly: “the reason why albumen does not dissolve off the sheet during processing is because contact with silver nitrate in the sensitizing bath coagulates it and forms a new insoluble silver-albumen complex called silver albumenate. This substance itself is light sensitive and makes an important contribution to image formation in albumen paper.”

And job three is coupled to the others through one variable, in the wrong direction. Reilly:

If the silver bath is very strong, the coagulating effect of silver nitrate on the albumen layer is correspondingly strong, and the solution will not permeate through the albumen very quickly. This means that a longer time of floatation is required for albumen paper on strong sensitizing solutions. On the other hand if the silver solution is relatively weak, then prolonged floating may be detrimental because the albumen — which is water soluble unless coagulated — may begin to dissolve off the sheet before it is completely coagulated.

Which is why a fresh bath behaves worse than a used one. The double replacement leaves ammonium or sodium nitrate in the solution, and those salts coagulate albumen too. A bath that has silvered fifty sheets has accumulated them; one mixed this morning has none, and Reilly records the dissolving-off problem as “especially noticeable with freshly made-up sensitizing baths” for exactly this reason. Old manuals advised adding the nitrate on purpose — advice he bounds carefully to silver-poor baths of 5 to 8 per cent, “not applicable when a bath of 10 % strength is used.”

Why the sensitised sheet will not keep

Reilly’s figures are 24 to 48 hours “depending on environmental conditions”, and in extremely humid and warm conditions the sheets “may yellow in a matter of 8 to 12 hours, or even less”. The mechanism is spontaneous reduction: organic matter in the layer slowly reduces silver to the metallic state without any light at all, and finely divided metallic silver is yellow. The same reaction browns the bath.

Citric acid is the historical answer and it is a trade, not an improvement. Five per cent citric acid in the silver bath gives the maximum preservative effect; as little as 1 per cent extends usable life noticeably. What it costs on glossy albumen is stated plainly: the print colour becomes reddish brown “even with prolonged gold toning”, and purple tones become difficult. Reilly notes that professionals in the 1870s and 1880s went on sensitising their own paper for exactly that reason, even after ready-sensitised paper existed. The idea of using a large amount of citric acid to preserve albumen paper was published in 1869 by a Viennese photographer, Adolf Ost; the first commercial “ready sensitized” albumen paper followed in 1872, from the Sensitized Paper Co. of Portsmouth, Ohio.

Two practical consequences. Citric acid is replenished on volume lost, not on silver consumed — a litre that had 5 per cent citric acid and is down to 850 mL takes 7.5 g of citric acid with its replenishment silver. And a sheet you have deliberately preserved must be kept scrupulously out of white light, “because the slightest exposure to actinic light forms some metallic silver that acts as a catalyst for further silver reduction.”

Ammonia fuming: what it did, and why there is no procedure here

☠Fuming — the chemistry and the history, and nothing to follow

What it was. Reilly: “a procedure in which the sensitized and dried sheets of albumen paper were hung in a closed box and subjected to the vapors of ammonia. The ammonia fumes were supplied by placing strong ammonia in a dish in the bottom of the box. ‘Fuming’ was usually carried on for 5 to 10 minutes. The purpose of fuming was to make the paper more sensitive and to obtain richer, more brilliant prints.”

Why it worked, as far as the sources go. Fuming is the vapour version of the ammonia-nitrate process, and Reilly dates the parent observation to 1840: adding ammonia to a silver bath until the brown precipitate just redissolves “causes a more brilliant, vigorous image in salted papers”, and it suited weak negatives. The ammonia-nitrate bath had two faults, and the second is why albumen printers reached for the vapour instead: the prints yellowed very quickly, and on albumen the alkaline bath “tended to dissolve the albumen off the paper”. Neutralising it with nitric acid worked but merely formed ammonium nitrate, which accumulates anyway, so Reilly judges that route “doubtful” and concludes that “fuming seems to be a better way to produce the advantages of ammoniacal silver.”

Where it was practised. It was common in the United States and “hardly practiced at all in Europe”. Reilly’s resolution of that geographical puzzle is the useful part: “much of the value of fuming may be realized by simply increasing the strength of the silver bath or by aiming for negatives of slightly different density range.” Fuming mattered most when a low-chloride paper was sensitised on a weak bath — the 8 to 9 per cent baths of 1880 to 1900 — and a stronger bath buys most of the same sensitivity for slightly more silver. Where the practice became customary, everything else adjusted to it and it came to look necessary.

Why this course gives no procedure. A dish of concentrated ammonia evaporating in an enclosed volume for five to ten minutes is a deliberate vapour generator. HSE’s EH40 sets ammonia at 25 ppm (18 mg/m³) over eight hours and 35 ppm (25 mg/m³) over fifteen minutes, and Chemical Safety Card 0215, quoted on the ammonia solution page, records that harmful contamination of the air “can be reached very quickly on evaporation of this substance at 20 °C”. The recognised control for that is engineered extraction, which is a Level C facility. No source read for this course publishes the vapour concentration inside a fuming box, so the course cannot even tell you how far above the limit it would be — which is itself a reason not to publish a method. And there is a second hazard specific to this bench: ammonia and silver nitrate together can form fulminating silver, and Reilly gives that warning himself while declining to describe the “boiling down” procedure that provokes it.

And Reilly’s own verdict on the practice. “For the modern practice of albumen printing, the troublesome and unpleasant process of ammonia fuming seems unnecessary.” A standard reference on this exact process, writing before anybody was arguing about it, reached the same conclusion this course reaches for a different reason. Increase the silver bath instead; that is the substitute the source itself offers.

Why the fixer is neutral to alkaline, and never an acid hardening fixer

Reilly’s own two reasons are stated and are both about the layer: 2 g of sodium carbonate per litre “promotes more effective fixation and helps to prevent the blistering of the albumen layer on heavily albumenized papers.”

The third reason is general printing-out chemistry and Reilly supplies it from a different chapter. The sel d’or method of the 1850s mixed gold chloride and hypo together, and “in many cases the acidity of the gold solution decomposed the sodium thiosulfate and liberated sulfur, which ultimately caused the prints to fade.” Acid plus thiosulfate liberates sulfur; sulfur attacks finely divided silver; an albumen print already has more retained silver than any other printing-out paper. Bringing an acid fixer to that layer is bringing the sel d’or failure back in a different bottle.

And the fourth is an absence rather than a finding. An acid hardening fixer contains alum. No source read for this part tests an alum hardening fixer on an albumen print, so the course does not claim it has been shown to damage one. What it says is narrower and sufficient: the fixer that the standard reference on this process publishes for it contains no hardener, is deliberately made alkaline, and gives two stated reasons; use that one.

!A place where two sources describe the same 1855 report differently

The AIC’s conservation wiki summarises the Photographic Society of London’s Fading Committee as reporting that fading was caused by “imperfect washing of the prints; use of old or insufficiently acidic hypo bath; acidity of mounting materials; excessive moisture and sulfur in the atmosphere.”

Reilly quotes the committee’s own report directly, and it says something different: “the most ordinary cause of fading, may be traced to the presence of sulphur, the source of which may be intrinsic from hyposulphite left in the print, or extrinsic from the atmosphere, and in either case the action is much more rapid in the presence of moisture.” Its two practical recommendations were thorough washing and gold toning.

The course follows Reilly’s quotation of the primary document, and notes the discrepancy rather than smoothing it: a summary that has an albumen print fading for want of acid in the fixer points the opposite way from the mechanism every other source on this page describes, and the course could not resolve where the wiki’s phrase came from. Where a secondary summary and a quoted primary source disagree, the primary source governs.

Toning: why albumen needs four times the gold

Reilly’s figures are 0.1 to 0.2 g of gold chloride per litre for matte salted papers and 0.4 to 0.5 g per litre for glossy albumen, and his reason is transport rather than chemistry: “albumen prints need a much stronger and more effective toning solution than salted papers do, because albumen is less permeable and the silver particles are more protected. This also means that the toning of albumen prints is usually slower — even with a stronger toning solution — than the toning of salted paper prints.”

The mechanism is Part XXII’s and is not repeated. Two of its consequences are albumen-specific and belong here. The bath must not be made too strong to work faster, because “too rapid a deposition of gold will spoil the prints. The gold layer will then be merely superficial, and will be largely removed in the fixing bath, leaving a flat and meager looking print.” And an uneven coating shows up here before it shows up anywhere else: “any variations in the thickness of the albumen coating, especially in the case of double-coated papers, will be immediately apparent in the toning step, because less heavily coated areas will tone more quickly and deeply.”

3 Ag + [AuCl₄]⁻ → Au + 3 AgCl + Cl⁻

The acid case: one gold atom replaces three silver atoms, which is why an acid gold bath bleaches faster than it tones

Reilly’s theory chapter gives the reason an alkaline bath is used rather than an acid one, and the equation above is the case it argues against: in an acid gold bath “one atom of gold replaces three atoms of silver, a case in which toning action would lag far behind bleaching of the silver. The result would be a flat, lifeless image with a reddish color. In an alkaline toner the gold exists in a different ionic form and there is a more favorable substitution of one atom of gold for one atom of silver.” No equation is given here for the alkaline case, because Reilly names no species for it — “a different ionic form” is as far as he goes — and writing one down would be inventing the chemistry this course exists not to invent.

Data to record

Use the lab notebook and the exposure log.

The sheet. Coating batch number, single or double coat, hardening route, date coated, and how it was conditioned.

The sensitising. Bath strength and how it was determined — mixed strength, a Volhard titration, or replenished by rule of thumb. Citric acid, if any, and at what per cent. Bath temperature and volume. Float time, timed from when. How many sheets that bath had already served, and its colour before and after. Drying: hung or flat, warm air or not, elapsed time, and how long between drying and exposure.

The exposure. Source, distance, and dose if you have one; or date, time, sky and orientation if you used the sun. Elapsed time. Number of inspections. What the margins looked like when you stopped, in your own words, and specifically whether they had bronzed.

The processing. First wash time and changes. Toner formula, gold concentration, temperature, time, and what the print looked like by transmitted light when you stopped. Fixer strength, carbonate, times in each bath, and how many prints those baths had already fixed. Washing aid, final wash time, and every bath’s temperature.

The measurement. Maximum density from the densitometer, on the dried print. Exposure scale from a step tablet printed alongside. Image colour, described and, if you can, measured. Surface: gloss, judged in raking light against your salt print.

The atlas row. Part XXV’s comparison atlas wants exposure scale, maximum density, image colour, surface, cost and difficulty for this process as you ran it, on your standard negative. Fill it while the prints are in front of you.

And the untoned control, described beside the toned print. That comparison is the record of what toning is worth, and it exists only if you made one.

Analysis

Compare your albumen print with your salt print from the same negative, side by side, in the same light, and account for every difference in physical or chemical terms. The binder lesson predicts higher maximum density, cleaner whites, gloss, more apparent sharpness and a shorter exposure scale — so a negative that suited the salt print may have blocked up here.

Then compare the toned print with the untoned one — the colour change, the density change, and the difference in how the two look by transmitted light.

Then read the numbers against Hübl, who found glossy albumen’s scale length equal to platinum’s and salted paper’s longer than both. Does your step tablet agree? If your albumen scale is longer, something is wrong with the comparison, and the first thing to check is whether both reached maximum density.

And ask the diagnostic question about your own coating. Thin areas tone faster and deeper, so the toned print is a map of the coating: hold it up and look for gradients running in the direction the sheet hung to dry.

Troubleshooting

What you see	Likely cause	What to do
The layer came off in the silver bath	The float ran long, the bath was warm, the tray was agitated, or the bath was fresh and weak	The troubleshooting entry has the full diagnosis. Shorten the float, check the bath is at 21 °C, do not rock the tray, and remember that a fresh bath is the dangerous one
Paper-white circles with hard, definite edges	Air trapped under the sheet during the silver float: those areas were never sensitised	Break every bubble before the clock starts, and check the underside of a thick sheet
Blotches or pale spots in the dense areas — the old manuals’ “measles”	Insufficient sensitisation: a too-weak bath, or too little residual sensitiser in the paper	Nothing helps an exposed sheet; unexposed ones may be re-floated on a stronger bath
Uneven density in patches, worst near one edge	Silver reached the back during the lift, or the runoff was not blotted	Peel more slowly, drain over the tray, blot the low corner
A metallic marbled sheen on the exposed print	Surface scum on the silver bath	Filter the bath, and draw a folded blotting-paper strip across the surface before each sheet
The bath has gone nearly black	Dissolved organic matter reducing silver to the metallic state	15 g of kaolin per litre, shaken in after each session and settled overnight; decant off the clear solution
Blisters in the layer during processing	A jump in temperature or pH between baths, worse on heavily coated sheets	Everything at 21 °C, and 2 g of sodium carbonate per litre in the fixer. Reilly: if blisters keep appearing despite this, something in the rawstock is reacting and a different paper is needed
The print toned quickly, then went flat and thin in the fixer	The toning bath was too strong, so the gold went on superficially and the fixer took it off	Weaker bath, longer time. Reilly wants ten to fifteen minutes or more
The print went slate blue and lost density	Over-toned: too much gold substituted for silver	Stop before it looks at all bluish. Judge by transmitted light and stop when the last warm colour has almost gone
The toner stopped working with plenty of gold left in it	A one-use alkaline bath that has gone inactive, or a trace of fixer in it	“There is no clue other than the cessation of toning action.” Mix fresh, and check your tray discipline
Prints in one batch toned to different degrees	They do not tone at the same rate, and coating variation shows here first	Tone fewer at a time. Reilly says the number that can be toned at once is limited by exactly this
The finished print is weak, flat and reddish, with no purple obtainable	Citric acid in the bath or in the albumen	Reilly’s stated trade: citric acid makes the print reddish brown “even with prolonged gold toning” and makes purple tones difficult. Take it out if you want purples
Brown spots or foxing appearing weeks later	Residual silver nitrate not washed out, or insufficient fixing and washing	Bostick & Sullivan name this failure specifically. It is the argument for their long first wash; see the contested callout above, and run a residual-silver test
The dried print curls into a tube and cracks when you flatten it	A thick albumen layer on thin paper, dried out completely	Mount it damp, or rewet and blot before mounting. Never dry mount, and never force a bone-dry sheet flat

Clean-up

Collect before you clean. Every tray on this bench holds silver except the last wash, and the first wash holds more of it than anything else. Bottle, label and date each stream through the silver-bearing waste SOP and the labelling SOP before anything is rinsed.

Return the silver bath to its bottle, add about 15 g of kaolin per litre, shake, and leave it overnight. Bostick & Sullivan’s version is half a teaspoon after every session, settling in 12 to 16 hours, and filtering before the next.

Wash the trays in cold water and keep them marked. Silver stains everything, and a tray that has held fixer must never hold toner.

Wash your hands immediately, whether or not you think you touched anything. Reilly’s instruction is unconditional and the reason is argyria.

And check the bench and the floor under the trays with a light. A silver spill you do not find tonight is a black stain tomorrow and a contamination source for months.

Storage

The sensitised sheet does not store. Twenty-four to forty-eight hours, less in heat and humidity, and Reilly’s blunt summary is “for best results it is necessary to sensitize, print and process all on the same day.” Plan the session so that every sheet you sensitise is exposed and processed before you stop.

The silver bath stores well and improves slightly with use, in a brown bottle, with the kaolin in it, decanted off the clay before each use. Bostick & Sullivan give an unused 15 per cent solution a shelf life of ten years and more.

The gold toner does not store made up. Reilly: most alkaline baths are intended for one-use toning “and become inactive spontaneously after a few hours”; Bostick & Sullivan give their working toner a usable life of twelve to sixteen hours and say to mix fresh for each day’s printing. Baths made with sodium acetate can be strengthened and reused, which is the exception.

The fixer is made fresh on the day of use, both baths, and its capacity is the number that decides whether the print survives. Reilly reports that the literature suggests up to 150 8 × 10 prints per litre of 15 per cent thiosulfate, and then recommends “no more than 10 to 15” for optimum permanence — an order-of-magnitude gap between what a bath will do and what it should be asked to do, because “the silver content of printing-out papers is very high relative to conventional develop-out materials”. Against the cost of the silver on this page, fixer is free.

The finished print stores flat, and its enclosure is a decision with evidence behind it — which is the next page, where the conservation sources disagree with each other and the disagreement is instructive.

Disposal considerations

Everything on this bench except the last wash water is silver-bearing, and silver is the reason. Silver nitrate carries H410, very toxic to aquatic life with long-lasting effects, and a spent fixing bath carries dissolved silver-thiosulfate complexes. The general chemistry is that silver can be precipitated out of a wash stream — Reilly’s own nineteenth-century method was to add sodium chloride or sodium carbonate and let the silver chloride or carbonate settle — and that spent fixer is concentrated or reduced for a refiner.

The gold toner carries a precious metal and, on the thiocyanate formula, a substance that must never meet acid. It is bottled separately and labelled with what is in it, and no acid goes near that bottle.

Bostick & Sullivan publish two disposal instructions this course does not adopt as its own. They tell the reader to send used and unused gold toner into the sewer, and albumen solution the same way with plenty of cold water. The course reports what the maker says and does not repeat it as an instruction: a gold toner that has toned prints contains silver chloride from the substitution as well as gold, and a jurisdiction’s discharge consent is not something a manufacturer elsewhere can speak for. Their third instruction the course does follow — silver nitrate and exhausted fixer as hazardous waste — along with their home neutralisation route for fixer, which is metallic replacement on steel wool and is Part XII’s subject.

Local regulation governs. The course can tell you the chemistry and the general practice; it cannot tell you what your discharge consent says. See the disposal ruling and the general chemical waste procedure. Check your local regulations.

Questions

1. State the three jobs the silver bath does on an albumenised sheet. Which of them does a plain salted paper not ask of it, and what follows for the float time?

2. Reilly says a stronger silver bath needs a longer float. Explain the mechanism in two sentences, and then say what happens instead if the bath is too weak.

3. A printer mixes a fresh 12 per cent bath and loses the layer off the first three sheets, then has no further trouble for the rest of the session. What changed, and what could they have done to the first bath?

4. You have printed until the shadows are just bronzed. Reilly says albumen needs about one and a half stops of overprinting and salted paper about two. Why does a printed-out image need overprinting at all, and why does albumen need less of it than salted paper?

5. Two sources tell you to wash the exposed print for ten minutes at most and for at least twenty-five. Give each one’s reason, say which you would follow and why, and describe an experiment that would settle it.

6. Explain to somebody who has only ever used a rapid fixer why this print goes into two baths of plain thiosulfate rather than one bath of a hardening fixer, and give three separate reasons.

7. Ammonia fuming raised the speed and contrast of albumen paper and was standard practice in American studios. Give the chemistry, the reason this course teaches it and gives no procedure, and the substitute Reilly himself offers.

8. Your gold toner has stopped working and there is plenty of gold in it. Give three causes and say how you would tell them apart.

Further experiments

Float time series. Sheets from one coating batch, floated on one bath at 1½, 2½, 3½ and 5 minutes, everything else held. Reilly predicts the short one is under-sensitised — look for the “measles” in the dense areas — and that the long one risks the layer. Print all four from the same negative and measure maximum density.

The prediction the design asks for, and it is worth writing down first. Predict what will happen if the sensitising float runs to twice the specified time, and state which observation would confirm it before the sheet is ruined. The observation is available and most people miss it: watch the bath, not the sheet. Cloudiness or drifting strands under the sheet mean the layer is going into solution, and you can lift the sheet at that moment and still have most of a coating.

Bath strength against float time, crossed. Two baths at 10 and 15 per cent, three float times each, one coating batch, one negative. Reilly predicts the optimum float moves longer as the bath gets stronger, and Bostick & Sullivan’s six minutes on 15 per cent sits at one corner of that grid.

Fresh bath against seasoned bath. Reilly attributes the dissolving-off problem to the absence of accumulated nitrates in a fresh bath. Split one litre in two, add ammonium nitrate to one half at a concentration you calculate and record, and float sheets from the same batch on each. This is a deliberate departure from Reilly’s own advice — he says the nitrate addition was for silver-poor baths of 5 to 8 per cent and is not applicable at 10 — so the interesting result is the one where he is right and nothing changes.

The first-wash question, settled on your bench. Two prints from one sensitised batch, exposed identically, one washed to Reilly’s ten-minute cap and one to Bostick & Sullivan’s thirty. Tone them in the same bath, together, and record the toning time each needs and the final colour. Then run the residual hypo and silver tests on both. This is a real open question and a real answer to it would be worth publishing.

Toning series. Five prints from one negative, pulled from the toner at 3, 6, 9, 12 and 15 minutes, plus one untoned. Measure maximum density and describe the colour of each, wet and dry: Reilly’s three warnings — density loss on over-toning, the slate blue, and the gap between the tray and the dried print — are all visible in one strip of six. Carry the single and double coated halves of the coating lab’s batch through the same series and record the toning time each needed.

And the one nobody has published. Reilly wrote in 1980 that “experimental evidence on the washing of albumen and salted paper prints is almost nonexistent”. A residual-thiosulfate series on albumen prints — wash time against measured residual — is within reach of Part XII’s methods and would be a genuine contribution rather than an exercise.

Check your understanding

Question 1. Why does a stronger silver bath require a longer float on albumenised paper, when a stronger bath would sensitise any other salted paper faster?

• Because a stronger bath is more viscous and penetrates the layer more slowly
• Because silver nitrate coagulates the albumen, and a stronger bath coagulates it faster, so the solution then has to permeate a layer it has already sealed
• Because the excess silver has to be washed back out again afterwards
• Because a stronger bath cools the sheet and slows the reaction

Show the answer and why

Answer: Because silver nitrate coagulates the albumen, and a stronger bath coagulates it faster, so the solution then has to permeate a layer it has already sealed

The silver bath is doing three jobs and the third one fights the first two. Reilly: "If the silver bath is very strong, the coagulating effect of silver nitrate on the albumen layer is correspondingly strong, and the solution will not permeate through the albumen very quickly." The opposite failure sits at the other end: a weak bath permeates readily but may let the water-soluble albumen dissolve off the sheet before it has been coagulated at all.

Question 2. A printer mixes a fresh 12 per cent silver bath, and the albumen layer comes off the first two sheets. By the fifth sheet the problem has gone. What changed?

• The bath warmed up to room temperature
• Ammonium nitrate from the double replacement accumulated in the bath, and it coagulates albumen too
• The bath weakened, so it coagulated the layer more gently
• The later sheets had dried more thoroughly

Show the answer and why

Answer: Ammonium nitrate from the double replacement accumulated in the bath, and it coagulates albumen too

Reilly identifies this precisely: the dissolving-off problem is "especially noticeable with freshly made-up sensitizing baths, because the sodium or ammonium nitrate which accumulates in older baths as a result of the double replacement reaction involved is absent when a bath is fresh. These salts also have a coagulating effect on albumen." Some old manuals added the nitrate deliberately — advice Reilly bounds to silver-poor baths of 5 to 8 per cent.

Question 3. Which of these are reasons this page gives for using a neutral-to-alkaline plain thiosulfate fixer rather than an acid hardening fixer? Select all that apply.

• Alkalinity promotes more effective fixation
• It helps prevent blistering of the albumen layer on heavily coated papers
• Acid decomposes thiosulfate and liberates sulfur, which is what ruined the prints of the sel d’or era
• Alum has been shown by accelerated ageing to crack the albumen layer

Show the answer and why

Answer: Alkalinity promotes more effective fixation, It helps prevent blistering of the albumen layer on heavily coated papers, Acid decomposes thiosulfate and liberates sulfur, which is what ruined the prints of the sel d’or era

The fourth is the one this page explicitly declines to claim: no source read for this part tests an alum hardening fixer on an albumen print, so the course does not say it has been shown to damage one. The first two are Reilly’s own stated reasons for the 2 g of sodium carbonate per litre. The third is his account of why the sel d’or combined toning-and-fixing method faded so many prints — the acidity of the gold solution decomposed the thiosulfate and liberated sulfur.

Question 4. You compare your albumen print with your salt print from the same negative. Which differences follow from the binder rather than from the silver chemistry?

• The albumen print reaches a higher maximum density
• The albumen print is visibly glossy
• The albumen print needed a stronger gold toner and took longer to tone
• The albumen print is a printing-out image made by light alone with no development

Show the answer and why

Answer: The albumen print reaches a higher maximum density, The albumen print is visibly glossy, The albumen print needed a stronger gold toner and took longer to tone

The fourth is the chemistry both share, and it is Part XXII’s subject. The first three are all the layer. Density and whites: the image is in a compact transparent layer instead of scattered among fibres. Gloss: a smooth coagulated protein top surface. Toning: albumen is less permeable and the silver particles are more protected, so Reilly’s bath for glossy albumen carries four to five times the gold of a matte salted paper’s and still tones more slowly.

Question 5. Reilly reports that the literature suggests up to 150 8 × 10 prints can be fixed in a litre of 15 per cent thiosulfate, and then recommends no more than 10 to 15. What is the difference between those two numbers measuring?

• The first is for salted paper and the second for albumen
• The first is the point at which fixing visibly fails; the second is the point beyond which permanence is compromised
• The first is for a single bath and the second for two-bath fixing
• The first is a nineteenth-century figure and the second a modern one

Show the answer and why

Answer: The first is the point at which fixing visibly fails; the second is the point beyond which permanence is compromised

Capacity and exhaustion are not the same quantity, which is one of the terminology pairs this course keeps apart. A bath will go on clearing prints long after it has stopped clearing them well enough for a print to last, and Reilly’s reason for the conservative figure is that "the silver content of printing-out papers is very high relative to conventional develop-out materials" and the colloidal silver image is vulnerable. Against the cost of the silver on the sheet, fresh fixer is the cheapest permanence you can buy.

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