Lab: Printing, Toning, Fixing and Washing a Salt Print

Purpose

To take a sensitised sheet from the previous session through to a finished, toned, fixed and washed print — and to measure the two numbers no book can give you: how much density your own fixer takes off your own print, and whether your own wash actually removed the thiosulfate.

Three things make this session unlike every printing session so far. The exposure is judged by looking, because the image forms during it. The correct exposure looks wrong, because the print must be made darker than it will finish. And the fixer is an adversary as well as a necessity, so it is weaker, shorter and more alkaline than anything in Part XI.

No quantity here is new. The gold toners, the plain fixer, Reilly’s alkaline bath and the sulfite washing aid all live in the formulary with their provenance and the function of every ingredient.

Learning objectives

By the end of the session you will be able to:

• Expose by inspection through a split-back frame, and recognise the appearance a printed-out image must reach before it comes out.
• Tell an exposure change from a drying change while a print is still in the frame.
• Say what the milkiness in the first wash is, and use its disappearance as the end point.
• Tone a print by eye, name what each colour stage is chemically, and choose a stopping point you can defend as a picture decision.
• State why this fixer is weak, brief, plain and alkaline, giving a separate reason for each of the four departures from Part XI.
• Predict what an acid or rapid fixer would do, and why the damage is worse here than on any other material in the course.
• Run a two-bath fix and explain why a second bath is a chemical requirement rather than a margin.
• Measure your own fix-down in density and in steps of a wedge, and use it to set the next exposure.
• Test the finished print rather than assuming it, and say what a positive result means on a paper with no baryta layer.

Prerequisites

• Lab: salting and sensitising a sheet of paper — you need its sheets, and they keep a day or two.
• Gold toning and the permanence of a printed-out silver image — the chemistry of the bath you will be standing over, and the rule that thiourea and platinum toners are not given as procedures.
• Printing out: silver chloride made and darkened in the paper, particularly its account of what the fixer does and why the first wash is not optional.
• Fixer formulations and types and fixer capacity and exhaustion, because almost every rule of thumb in them is suspended here and you should know what you are suspending.
• Wash testing lab and the residual hypo and silver tests SOP — the tests are applied here to a material they were not designed for, and the page says exactly what that costs.
• Build a contact printing frame, with a split back. It is not a convenience here; see Equipment.

Safety classification

Level B, and three hazard groups combine. The rubric assigns the level from the procedure as written.

Silver nitrate, unreacted, is on every sensitised sheet and in every drop of the first wash. It carries H314, causes severe skin burns and eye damage, with H272 as an oxidiser and the aquatic hazard statements, at signal word Danger. It stains everything permanently, and the first wash is the most concentrated silver-bearing solution this course produces.

The gold toner contains a gold(I) complex and, in the thiocyanate version, a thiocyanate salt. Chloroauric acid is Level B in this course’s encyclopaedia; so is sodium thiocyanate, and its level is carried as much by an incompatibility as by a toxicity.

Ultraviolet, either from the Part XVI unit with its enclosure and interlock, or from the sun for an hour at a time.

⚠The absolute rule of this bench: no acid meets the thiocyanate

Acidifying a thiocyanate releases hydrogen cyanide. The International Chemical Safety Card for sodium thiocyanate records a violent reaction with acids, and the old EC classification quoted on the same card carries R32, “contact with acids liberates very toxic gas” — the gas being hydrogen cyanide. The sodium thiocyanate page sets the ruling out in full.

What that means for this session, concretely. No acid stop bath, no acid or rapid fixer, no citric acid clearing bath, no vinegar, no acidic descaler, and no acid waste bottle anywhere in the room while the toner is out. That is not an inconvenience here, because the process wants none of them anyway: the fixer is plain and alkaline, there is no stop bath, and the clearing agent is sulfite. The rule costs you nothing and removes the failure mode entirely.

The place it actually goes wrong is the waste container, exactly as it does with ferricyanide in Part XXI. Nobody plans to pour acid into a spent thiocyanate toner. They top up a part-used bottle whose label they did not read. Label everything, under the labelling SOP, and never use the unlabelled container route.

And there is a test in this session that brings an acid into the room. The residual thiosulfate test uses a reagent containing acetic acid. It is done on a thoroughly washed print, at the end, after the toner has been bottled and the bench cleared — and the sequencing is a control, not tidiness. It is written into the procedure at Stage 9 for that reason.

⚠What is not a hazard here, and why saying so is worth the space

The fixer is not the fixer you are used to, and its hazards are milder. There is no acid hardening bath, no ammonium thiosulfate, no sulfur dioxide evolved from an acidified sulfite. The bath is sodium thiosulfate in water, optionally with 2 g of sodium carbonate per litre, at 5 to 15 per cent, at room temperature. Its risk profile in this session is dominated by the dissolved silver it accumulates, not by the thiosulfate.

Ventilation is not among the controls, because no step evolves a vapour or a gas. No stop bath, no acid, no heated bath, nothing volatile. The section below says what the control actually is.

And there is no chromium(VI). Both bought kits ship a potassium dichromate contrast solution and both explain how to use it. This course does not, at any concentration: chromium(VI) compounds carry carcinogenicity, mutagenicity and reproductive-toxicity classifications, and the chromium ruling excludes them entirely. The chemistry lesson gives the four contrast levers used instead — chloride concentration, citrate, binder and light source — which are the ones Reilly himself recommends over chromates in any case. If your kit contains the dichromate sachet, leave it sealed and dispose of it as the supplier’s own sheet directs.

None of that softens the two real hazards, which are the silver nitrate’s eye statement and the acid-and-thiocyanate rule above.

Hazards

Hazard	Where it arises	Control
Severe eye damage (H314) from silver nitrate	The sensitised sheet, the frame, the first wash, and every drip between them	Chemical splash goggles, not spectacles, from loading the frame until the first wash is bottled
Hydrogen cyanide, if the acid rule is broken	A thiocyanate toner meeting any acid, in the tray or in the waste bottle	The rule above, absolutely. Separate labelled waste for the toner. No acid in the room
Skin contact with the toner	Every tray transfer	Nitrile gloves. Bostick & Sullivan’s own line: wear gloves and minimise exposure to the toning bath. Gold chloride stains skin purple, and Photographers’ Formulary note that the stain is gold bound to skin protein and cannot be removed chemically
Ultraviolet to eye and skin	Every minute the lamp is on, and the whole of a sunlight exposure	The Part XVI unit’s enclosure and interlock; outdoors, shade for the frame where possible, covered arms, a hat, eyes off the sheet. Bostick & Sullivan’s own instruction is to inspect indoors when printing in sunlight, which halves the exposure as well as the fogging
Dissolved silver in the fixer and the toner	By the end of the session both are loaded with it	Both collected, both labelled, neither to the drain. Silver-bearing waste SOP
Sulfide reagent for the residual silver test	Stage 9 only	Kept away from every acid on the bench and used with ventilation; a drop on a test strip, not a tray. The test SOP governs
Permanent staining of everything	Throughout	The silver stains black and the gold purple. Blotter down, trays on a spill tray, an apron
Glass breakage in the frame	Loading, and a cold frame put into sunlight	The glass handling SOP. Reilly warns that many negatives have been shattered in printing frames from too much pressure, or cracked by expansion in sunlight in an overstressed frame

Required PPE

Chemical splash goggles for the whole wet sequence. The silver nitrate eye statement governs, and the first wash is where a wet sheet is lifted repeatedly at bench height.

Nitrile gloves throughout, and the print handled by its back and edges only. That last is Bostick & Sullivan’s instruction and it protects the print as much as you: a fingerprint on a sensitised or part-processed sheet prints as a fingerprint.

An apron. Silver stains black, gold stains purple, and neither comes out.

Sun protection if you print outdoors, which is protection against the exposure rather than against a chemical: shade for the frame, covered arms, and inspection done indoors.

No respiratory protection is specified for the printing and processing steps, because nothing in them raises a dust or a vapour. The one step where ventilation is a named control is the sulfide reagent at Stage 9, and it is controlled by ventilation and separation rather than by a respirator.

Ventilation

The control is separation, not airflow, for everything up to Stage 9. Nothing in the exposure, the washes, the toner or the fixer evolves a gas at room temperature: there is no acid, no stop bath, no sulfur dioxide, and the fixer is neutral to slightly alkaline, which is one of the two reasons Reilly gives for the carbonate in it. Work in a room with the ordinary through-draught HSE asks for wet photographic work, on a lipped and wipeable bench.

The step that does need ventilation is the residual silver test, because its reagent is a sulfide. Do it last, with the window open, away from the toner and from any acid, and follow the residual hypo and silver tests SOP.

And there is one airflow consideration that is about the print rather than about you. Reilly notes that neither the paper nor the frame should be excessively dry at the time of printing, because some moisture is needed for good sensitivity and contrast, especially with matte salted papers. A warm draught across a loaded frame on a windowsill is a slow print.

Materials

• Four to six sensitised sheets from the previous session, one of them a test strip cut into four or five bands, and one that has been kept as the K1 keeping-test sheet.
• A negative of long density range, the same size as the print, from the negatives lesson; and a 21-step transmission wedge if you have one, which changes this session from a print into a measurement.
• A 1 mil polyester spacer the size of the negative. Reilly’s precaution: silver nitrate transferred from a damp sheet to the emulsion of a negative causes red stains, and one thousandth of an inch of polyester between them prevents it without sacrificing sharpness. Photographers’ Formulary suggest a thin acetate sheet for the same purpose.
• Distilled water, 1 L, for the toner and for a final rinse if your tap water is hard.
• Blotting paper, clean fibreglass or plastic screen, silicone release paper, and a book press or weights.
• Test strips of your own paper, unexposed but sensitised and fully processed, for the residual tests at Stage 9.

Chemicals

Five baths, all from the formulary, at the volumes one session needs. Nothing here is a new formula; the working strength and the source of each is given so that you can see why they differ.

The gold toner — choose one.

Bath	Made from	Working strength	Source and character
Gold-thiocyanate	50 mL of 2 % ammonium thiocyanate and 50 mL of 0.2 % gold chloride, in water to 1 L	0.10 g/L gold chloride	Bostick & Sullivan’s published kit bath. Fast, ready when mixed, goes coldest — Reilly: “deep purple tending to black”. Bleaches before it tones, and must never meet an acid
Gold-borax	4 g borax and 8 mL of 1 % gold chloride, in warm water to 500 mL	0.16 g/L gold chloride	Photographers’ Formulary’s kit bath. Alkaline, gentler, warmer results, uses less gold. Needs to ripen; the yellow stock goes colourless when it is ready

Both sit inside Reilly’s range for a porous paper: 0.1 to 0.2 g of gold chloride per litre for arrowroot and plain salted papers, against 0.4 to 0.5 for glossy albumen. A matte paper tones quickly and would over-tone in the albumen bath.

The fixer — and this is where the sources disagree, so read the callout before you choose.

Bath	Composition	Time	Source
Plain thiosulfate	50 g sodium thiosulfate pentahydrate per litre — 5 % w/v	4 to 5 min, one bath	Bostick & Sullivan’s salted paper sheet. The Getty Atlas’s process description also gives 5 per cent
Reilly’s alkaline bath	150 g of the same salt plus 2 g sodium carbonate per litre — 15 % w/v	4 min plus 4 min, two baths	Reilly, for albumen and all salted papers
The Formulary kit’s own	50 g in 500 mL — 10 % w/v	10 min, one bath	Photographers’ Formulary’s P.O.P. kit

The washing aid. One per cent sodium sulfite: 10 g of sodium sulfite anhydrous per litre, used once and discarded, at no more than 20 prints of this size per litre.

And the first wash is water — several changes in a tray, or gently running water. Photographers’ Formulary specify a tray rather than running water so that you can see the cloud.

⁇Three published fixer strengths, from 5 to 15 per cent. Which?

They are not small differences, and the sources are all first-rate. Bostick & Sullivan and the Getty Atlas both give 5 per cent; Photographers’ Formulary give 10 per cent for 10 minutes; Reilly gives 15 per cent, alkaline, in two baths of four minutes.

The argument for weak is the image. A salt print’s silver is nanoparticulate and there is very little of it — Ware’s figure is about 3.3 mg in a whole plate at roughly a tenth of a modern print’s coating weight — so a fixer strong enough to be comfortable on a bromide paper is strong enough to take real density off this one. A weaker bath attacks less.

The argument for strong is the complexes, and it is a chemical requirement rather than a margin. Reilly’s account of the reaction is the one that matters: there are probably at least three different silver-thiosulfate complexes formed during fixation, thiosulfate must be present in excess or insoluble complexes form which cannot be washed out of the image layer at all, and one of those complexes is soluble only in fresh thiosulfate. A bath that is too weak or too far used does not under-fix visibly; it forms the complex you cannot remove, and the print fails years later.

What this page does. It gives Reilly’s two-bath alkaline 15 per cent as the archival route and the 5 per cent single bath as the kit route, and asks you to run one of them completely rather than inventing a third. Averaging two published procedures produces a procedure nobody tested. What resolves the disagreement in your own darkroom is not an argument, it is Stage 9: fix a strip each way, wash both identically, and test both. The measurement is the point of the session.

Two things all three sources agree on, and they are the ones that actually protect the print: fresh fixer for every session, because the high silver content of these papers exhausts a bath fast and even unused thiosulfate solution breaks down; and do not fix for longer than the time given, because prolonged fixation is, in Reilly’s words, much more injurious than is generally believed.

Why the carbonate, if you take Reilly’s route. Two reasons, both his. Slight alkalinity prevents any acid inadvertently introduced from decomposing the thiosulfate and liberating sulfur; and an acid fixing bath attacks the finely divided metallic silver of the image, bleaching the highlights and mid-tones, and that attack is minimised on the alkaline side. Two grams per litre is the whole addition.

Equipment

A split-back contact printing frame, and this is the one item with no substitute. Reilly’s description of why the back is hinged in two parts is the whole argument: one spring is loosened, half the back is opened and the progress of the exposure checked, while the still-closed half holds the negative and print in exact register. A felt or chamois pad behind the paper distributes the pressure and ensures contact over the whole area — Reilly notes that such pads were universal in the nineteenth century and that few people today know they exist. The frame should be at least one format larger than the negative, and glazed in double-thickness picture glass rather than window glass.

A UVA source, enclosed and interlocked, from Part XVI — or the sun, which is what the Alternative route below is about.

Five trays, larger than the print, labelled and reserved: first wash, toner, intermediate wash, fixer (two if you take Reilly’s route), final wash. Nothing metal, and no tray that has held an acid.

A timer, a thermometer, and — for the measurement — a densitometer reflection head if you built one.

Your working light, the same yellow incandescent as the last session. Reilly adds one refinement for this one: toning is judged in weak white incandescent light, not yellow, because you cannot judge colour under a yellow lamp — and he warns that judging a print lying flat in a tray is deceptive, so lift it and look at it against something.

Estimated cost

Band £££, and the driver is the gold rather than the silver. The capital is the frame, the UV source, the trays and the timer, all of which Parts XVI and XXI already asked for. What this session consumes is the silver already on the sheets — about £0.58 to £2.71 each at the planner’s dated figures, on the arithmetic in the salting lab — plus a litre of gold toner, a litre or two of fixer and some sulfite.

The fixer and the washing aid are the cheapest things on the bench, which is exactly why Reilly says to make a fresh batch every session: “compared to the other costs of albumen and salted paper printing, the price of fixer is cheap, and frequent renewal of the fixing bath is a worthwhile investment”.

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.

Consumed	This session	Sourced price	Cost this session
Silver nitrate, as coated on the sheets	about 1.2 g of AgNO₃ on five 8 × 10 sheets	£59.95 per 25 g to £112.90 per 10 g, 5 September 2026	£2.88 to £13.55
Gold chloride	0.1 g in a litre of toner; about 0.01 g leaves with each print, on the supplier’s own replenishment figure	Not priced. It is one of the gaps src/data/prices.json names, on the strength of this part’s own arithmetic	—
Sodium sulfite, anhydrous	10 g for a litre of washing aid	£13.68 to £19.98 per kg	£0.14 to £0.20
Sodium carbonate, anhydrous	2 g, if Reilly’s fixer is used	£7.20 per 500 g	£0.03
Borax, decahydrate	8 g, if the gold-borax bath is used	£9.98 per 200 g	£0.40
Nitrile gloves	2 pairs	£6.64 to £14.99 per box of 50 to 100	£0.27 to £0.60
Sodium thiosulfate pentahydrate	50 to 300 g, according to which fixer route	£14.70 per 1 kg of the raw salt, checked 7 September 2026	£0.74 to £4.41
Ammonium thiocyanate	1 g in a litre of the thiocyanate toner	Not priced	—
Cotton rag paper, as the sheets	4 to 6 sheets	Not priced. Hot-press cotton watercolour paper is a named gap	—
Distilled water	about 1 L	Not priced	—
Test reagents for Stage 9	a few millilitres of each	Not priced	—

The subtotal is a floor and not a total, and the missing rows are the important ones: gold has no price and paper has none either. What the priced rows do show is the shape — the processing chemistry other than the gold comes to about £1.60 to £5.60 a session, most of that spread being the hypo on the 300 g route, against several pounds of silver already on the paper and an unpriced quantity of gold on top.

Equipment is deliberately absent: a frame is not consumed and neither is a tray.

Waste streams

Four streams, all silver-bearing, and the toner is a fifth thing as well.

• The first wash — the most concentrated silver solution of the session, and the one the trade saved for recovery. Bottle it.
• The intermediate wash, dilute silver plus carried-over toner.
• The spent gold toner, which carries dissolved silver and the gold that did not deposit. Both are worth recovering and it gets its own labelled bottle, because it is the one container in the room that must never meet an acid.
• The spent fixer, heavily loaded with dissolved silver as silver-thiosulfate complexes by the end of the session — a different chemistry from the first wash and a separate bottle, as the salting lab sets out.
• The washing aid and the final wash water, dilute, and carrying whatever the print gave up.

The rule is the same as the last session’s and it does not depend on dilution: nothing containing silver goes to the drain. The silver-bearing waste SOP and the general chemical waste SOP govern, and local regulation is the only document that can answer the question for your drain.

Alternative route

This page declares requiresUV, and the alternative is the one the process was invented on.

Print in the sun. Reilly is unambiguous that daylight has accounted for all but a tiny fraction of the albumen and salted paper prints ever made, and remains the cheapest and most satisfactory source where mass production is not required; both kit sheets list sunlight first; the Getty Atlas’s own process description gives “perhaps 10 minutes in bright sunlight”. What you supply in place of a dose is a written record — date, time, sky, orientation, elapsed time and the appearance at each inspection — under the daylight exposure SOP and the outdoor exposure session SOP.

Three cautions belong with the offer, and all three are specific to this process rather than general.

A dull sky is not a slow sun. Ware reports the nineteenth-century observation directly: inadequate light levels produced weak prints regardless of how long the exposure ran, which is low-intensity reciprocity failure and cannot be compensated by time. Wait for a better day.

Below about 5 °C the paper loses sensitivity, so Reilly calls printing outdoors in winter practically impossible.

And never open the frame in the light you are printing by. Reilly’s instruction is exact: never open the frame to check the exposure in sunlight or open shade — bring it indoors to a room lit by a low-wattage white incandescent lamp, where the print can be judged with reasonable leisure and safety. Bostick & Sullivan give the same instruction for the same two reasons, fogging and your own ultraviolet exposure.

No frame with a split back. Two sheets of plate glass with clips will hold contact, which is what Bostick & Sullivan offer as an alternative, and you lose the thing this process most needs — inspection without losing registration. The workaround is a second, sacrificial coated strip beside the negative, exposed alongside, which you can uncover and look at without touching the print.

No densitometer. The fix-down can still be measured, less precisely, with a step wedge and your eyes: count the steps visible before processing and after, which is exactly what Photographers’ Formulary’s own calibration method does and is the origin of the “five steps” figure this page uses.

And one thing has no alternative at all. There is no version of this session that skips the washing. A salt print is washed before toning, again before fixing, again after fixing, treated in a washing aid and washed again — and Reilly’s own warning is that the base paper otherwise becomes a reservoir of image-threatening substances, because there is no baryta layer between the image and the fibres. If running water is genuinely unavailable, several changes of standing water with agitation is the historical method — Reilly records the nineteenth-century practice of squeegeeing the print, returning it to a fresh tray and agitating, repeated over a period that ranged from twelve hours in Abney’s recommendation to fifteen minutes in Haddon and Grundy’s — but you must then treat the wash as untested and run Stage 9’s residual thiosulfate test as a real experiment rather than a formality.

Preparation

Before the light goes on. Lay the trays out in sequence and fill them, because you will be carrying a wet print with two gloved hands. Make the toner: the gold-borax bath needs to ripen, so mix it the day before and check that the yellow has gone; the thiocyanate bath is ready when mixed, and Bostick & Sullivan note that the gold may momentarily go brown or orange as it is added before redissolving. Make the fixer fresh, today, and if you are using the Formulary’s 10 per cent version note their warning that the large crystals dissolve slowly, will not dissolve unless stirred, and want water at about 52 °C to start.

Check the negative and the frame. Clean both faces of the glass. Cut the polyester spacer. Reilly’s two precautions: the paper must be dry or silver will transfer to the negative and stain it red, and neither paper nor frame should be excessively dry, because moisture is needed for sensitivity and contrast. And do not put a cold frame straight into sunlight — unequal expansion of paper and negative gives a doubled image around the edges while the centre stays sharp.

Trim, if you are toning. Photographers’ Formulary’s one-line economy: trim the print’s edges before toning to conserve the gold. The toner works on the area you put in the tray.

And set the untoned control aside. Reilly’s advice for a beginner, and the most useful thing on this page: leave one print completely untoned, processed identically otherwise, as the basis of comparison. You cannot judge a toned print without one.

Procedure

Nine stages. Attended bench time is about three hours, of which more than an hour is washing, and the final reading is taken the next morning because a print judged wet is judged wrong.

The full sequence, with what leaves the print at each step

1. 11. Expose by inspection, past the point where it looks rightPrint-out: exposure and development are simultaneous. Stop at about half to two thirds of the final darkness, or when the shadows are just bronzed. Nothing leaves the print; silver chloride becomes silver, and chlorine is recycled by the excess silver nitrate
2. 22. First wash, in a tray, until the milkiness stopsOut: the unreacted silver nitrate, as a white cloud of silver chloride and carbonate formed by tap water. This is the recoverable silver, and skipping it wastes the gold and stains the print
3. 33. Gold toner, by inspection, 3 to 15 minutes at 17 to 21 °CIn: gold at the particle surface. Out: an equivalent amount of silver, which becomes silver chloride in the sheet — which is why fixing has to follow toning
4. 44. Wash, 3 to 5 minutes in running waterOut: carried-over toner. Reilly: interaction between fixer and toner changes the fixing solution in ways that damage the colour and the permanence of the print
5. 55. Fix — weak, brief, plain, and alkalineOut: the unexposed silver chloride, the silver chloride the toner just made, and — unavoidably — part of the image. Reilly two baths of 4 minutes, or the kit sheet 4 to 5 minutes in one
6. 66. Wash 2 to 4 minutes, then 1 per cent sodium sulfite for 3 to 4 minutesOut: the bulk of the thiosulfate first, then, by ion exchange, the part that water alone cannot shift
7. 77. Final wash, 30 minutes or moreOut: the sulfite and what it displaced. Longer for heavy stock; Reilly gives 40 to 50 minutes for the heaviest
8. 88. Dry, then flatten while slightly dampThe print gains density and goes colder as the layer contracts. This is when you find out what you actually made
9. 99. Test: residual thiosulfate and residual silver, on your own stripsThe only part of this sequence that tells you whether the wash worked. Done last, with the acid-containing reagent nowhere near the toner

Stage 1 — Exposure by inspection (30 to 60 minutes)

Load the frame under the yellow working light: glass, negative emulsion down, the polyester spacer, the sensitised sheet coated side down, the felt pad, the hinged back, springs locked.

Expose, and watch the margin outside the negative. Reilly’s guide is that it darkens first and reaches maximum density first, and that a good approach is to make the first check a short time after the margins appear to have got there. His end point is bronzing: when the margins begin to take on a greenish lustre, so much metallic silver has been reduced that a saturation point is reached and particles migrate to the surface to form a coherent shiny film. Many old manuals recommend printing until the shadows are “just bronzed”, and Reilly says that is correct advice for many negatives, especially ones printed in full sun.

Inspect properly. Open one spring, fold back half the frame, lift the paper by an edge and fold it back to look — the closed half is what keeps the registration. Do it indoors, away from the printing light. Bostick & Sullivan’s first inspection is at about three minutes and then every few minutes; adjust that to your own source.

=How far past 'right' — four sources, one instruction

Source	How they put it
Reilly	Overprint about two stops for salted papers, one and a half for albumen, with experience the only way to know precisely
Bostick & Sullivan	Stop when the print is one half to two thirds as dark as you want it to finish; it should be about three quarters as dark leaving the fixer
Photographers’ Formulary	Mark the lightest step of a step table that shows darkening; that step and usually four more are lost in washing, toning and fixing
Ware, reporting c. 1855 practice	Such prints “should be much overexposed to compensate for the inevitable loss in thiosulphate fixer”

Five steps of a 21-step wedge is 5 × 0.15 = 0.75 log H, which is 2.5 stops — within half a stop of Reilly’s figure, by a completely different method and from a completely different source. Expect two to three stops, and measure your own at Stage 8.

Stage 2 — Judging colour, and telling exposure from drying

This is the skill the page exists to teach, and it is easy to get wrong in a specific way.

What exposure does: the print darkens and the colour deepens from a faint grey through red-brown to a rich purplish or brownish black. Ware describes freshly printed-out silver from a Talbot-type sensitiser as exactly that — a rich, dense purplish or brownish black — and warns that the wet processing always shifts it to yellowish-brown, which “disappoints everyone who has ever made such a print”.

What drying does: the same print, allowed to dry out in the frame during a long exposure, also darkens and goes colder. Ware attributes that to coalescence ripening as the particles aggregate, notes that heat promotes it, and records that it was used to tone some early salt prints — which is why Talbot’s finishing step was a hot iron.

How to tell them apart. Three ways, in order of reliability.

Look at the margin, not the picture. The margin outside the negative receives the full exposure and dries at the same rate as the rest, so a change in the picture that is not matched in the margin is an exposure change, and one that appears everywhere at once is drying or warming.

Feel the frame. A frame that has been in the sun for twenty minutes is warm, and a warm sheet is a drying sheet.

And note the time of every inspection. A colour that has moved between two inspections five minutes apart in flat light and has not moved in the previous fifteen is telling you about the sky rather than about the print.

Stage 3 — The first wash (10 minutes)

In a tray, with changes, not under running water — that is Photographers’ Formulary’s instruction and the reason is that you need to see the water. Reilly’s version is about ten minutes in running water; Bostick & Sullivan give five to seven minutes with agitation every 20 to 30 seconds, or longer while the precipitate continues; the Getty Atlas says several rinses. All four end at the same place.

The end point is the cloud, not the clock. The first trayful goes white and milky. Change it. Keep changing it until a trayful stays clear. Photographers’ Formulary put the rule and its limit in two sentences: wash with additional trays of water until you get a trayful that is not cloudy, and do not over-wash, the image can be lost.

What the cloud is. Silver chloride and silver carbonate, being precipitated in the tray as the excess silver nitrate from the sheet meets the chloride and carbonate ions in your tap water — Reilly identifies the reaction in his sensitising chapter and then says explicitly that the clouding of the initial wash is that same reaction. Bostick & Sullivan describe it from the bench as a white milky cloud; the gold toning sheet describes a purple mist for a gelatin printing-out paper, which is the same reaction seen through a different binder.

And the print will lighten and go redder while it happens. Both are expected. Reilly attributes the reddening to swelling of the image layer, which changes the particle spacing.

Save this water. It is the most concentrated silver in the session, and it is what nineteenth-century printing operations recovered their silver from.

Stage 4 — Gold toning (3 to 15 minutes)

Into the toner directly from the wash, wet. Bostick & Sullivan note that a print going straight from the final rinse into the toner does not need drying first, and Photographers’ Formulary tone before fixing as standard.

Agitate constantly and watch the shadows. Bostick & Sullivan: the toner moves through the print in the shadows first, subtly changing the colour of those areas, and when you start to notice more dramatic changes the toning is nearly complete. Reilly’s temperature is 17 to 20 °C and the Formulary’s is 21 °C; his time is 3 to 15 minutes by inspection and theirs is 6 to 12 minutes.

Expect a thiocyanate bath to bleach first. Reilly explains it: thiocyanates dissolve silver chloride, so the print bleaches on entry and then intensifies as gold is deposited. Do not pull it at the bleach.

Judge in weak white incandescent light, lifting the print rather than looking at it lying in the tray, which Reilly says is deceptive. And carry the toning well past the point where a visible change first occurs — that is his instruction, and the commonest beginner’s error is stopping at the first sign of movement.

Stage 5 — Deciding when to stop

The colour is a continuum and the choice is yours. Bostick & Sullivan state the trade-off in one line: for cooler, bluer tones allow the print to tone until no further change is observed; for warmer red-browns, pull it earlier. The same negative, on the same paper, toned to two different points, is two different pictures — and this is the art-track decision of the part.

But you cannot see the answer yet, and every source says so. Photographers’ Formulary: it is difficult to judge the end result until the print is fixed, washed and dried, and the cold tone increases on fixing and drying. Bostick & Sullivan: the true final colour and density will not be observed until after the final fixing, rinsing and washing, and the toning can be faint until the print is fully dried.

Which is why the untoned control matters, and why the honest way to learn this is a set: tone one print to the first visible change, one to about half the total change, and one to exhaustion, process all three identically, and lay them beside the untoned one when they are dry. That is one session and it settles the question for your paper permanently.

Stage 6 — Fixing (8 to 10 minutes)

Wash first, 3 to 5 minutes in running water. Reilly’s reason is specific: interaction between the fixer and the toner may cause changes in the fixing solution that would damage the colour and the permanence of the prints. Photographers’ Formulary say no wash is needed provided the toning bath is not contaminated by fixer; take Reilly’s route, because the cost is five minutes and the failure is invisible.

Then fix, by whichever route you chose in Chemicals, and follow it completely.

• Reilly’s route: two trays of fresh alkaline 15 per cent, four minutes in each with constant agitation, drained at least five seconds between them, at 18 to 20 °C.
• The kit route: one tray of 5 per cent, four to five minutes with periodic agitation.

Why two baths is chemistry rather than caution. Reilly’s account: at least three silver-thiosulfate complexes form, thiosulfate must be present in excess or insoluble complexes form that cannot be washed out of the image layer, and one of the complexes is soluble only in fresh thiosulfate. The first bath does the bulk of the complexing; the second ensures that what is finally formed can be washed out. On a paper with no baryta layer, that second bath is doing its work in the fibres as well as in the image.

And do not exceed the time. Reilly twice: fixation is completed fairly rapidly and prolonged fixation is much more injurious than is generally believed, because thiosulfate that penetrates the fibres becomes almost impossible to remove.

✕What an acid or rapid fixer does here, and why the damage is worse than anywhere else

Reach for the bottle already on your shelf and you will lose the print. Three separate mechanisms, and they compound.

An acid bath attacks the image silver directly. Reilly gives this as one of the two reasons for the alkaline bath: an acid fixing bath tends to attack the finely divided metallic silver of the image, causing excessive bleaching of the highlights and middletones. On a developed print that attack is negligible because the silver is coarse; here the surface area is about a hundred times larger and there is a tenth as much silver.

An acid decomposes thiosulfate and liberates sulfur. Reilly’s other reason for the carbonate. Free sulfur on nanoparticle silver is the sulfiding reaction that the gold lesson shows costs about thirty times the density. Ware records what happened when the nineteenth century did this deliberately: Malone’s addition of nitric acid at the Reading establishment produced a “rich mulberry tint” and was probably one of the causes of the fading those prints became notorious for.

A rapid fixer is ammonium thiosulfate, and it is a stronger silver solvent still. Every argument above applies with more force.

And if there is thiocyanate in your toner, an acid fixer is a hydrogen cyanide problem as well as a print problem. The rule at the top of this page is absolute for that reason.

One historical practice that looks like an exception and is not. The “old hypo colouring bath” — deliberately decomposing the fixer to sulfide-tone the print — was widely used from about 1850 to 1858 and produced some prints that survive beautifully and many that had “totally perished or grievously faded” within a decade, in Thomas Sutton’s own words when he abandoned it in 1855. Reilly’s verdict is that control over the outcome is impossible in the routine course of printing. It is history, not a technique.

Stage 7 — Washing aid and final wash (35 to 55 minutes)

A short wash first, 2 to 4 minutes in running water. Reilly’s reason: this removes the vast bulk of the thiosulfate and avoids overloading the ion-exchange mechanism of the sulfite bath that follows.

Then 3 to 4 minutes with constant agitation in 1 per cent sodium sulfite. Used once and discarded, at no more than 20 prints of this size per litre — the same rate of exhaustion as the fixer.

Then wash for at least 30 minutes, in a washer where the flow reaches the whole print surface and the entire volume changes at least every five minutes. Reilly’s extension for heavy stock is 40 to 50 minutes. Where more than two prints share a tray with a siphon, hand agitation is absolutely necessary — that is his word.

⚗Why a plain paper washes differently from the fibre papers of Part XII

Part XII taught washing on a fibre-base silver gelatin paper, where a substratum of baryta and gelatin separates the image layer from the paper base. Two things follow from removing that layer.

The image is in the reservoir. Reilly: with albumen and salted papers the silver image is in much more intimate contact with the paper fibres, so both proper fixation and effective washing are needed to ensure that the base paper does not become a reservoir of image-threatening substances. In a baryta paper the thiosulfate in the base has a barrier to cross; here it does not.

But the image layer is more open. Reilly’s other observation cuts the other way: the removal of thiosulfate is affected by the diffusion rate through the image layer, so albumen probably takes substantially longer to wash than arrowroot or plain salted paper, which have more porous image layers. A plain salt print is among the easier things in this cluster to wash — the difficulty is that the consequences of not washing it are worse.

And water alone will not finish the job on any of them. Reilly: the rate of washing slows tremendously at low thiosulfate concentrations, and in practice it is impossible to remove every trace by washing in water. That is what the sulfite bath is for — it displaces absorbed thiosulfate ions and replaces them with more soluble and less harmful ones.

The honest limit. Reilly states that experimental evidence on the washing of albumen and salted paper prints is almost nonexistent, and that his recommended times are extrapolated from what is known about gelatin prints on the assumption that the same factors apply. This course has found no later study that closes that gap. Which is why Stage 9 is not optional.

One more caution from the same chapter, in the other direction: some papers may be injured by prolonged washing, the image layer beginning to dissolve, in which case a shorter wash is indicated. And Photographers’ Formulary warn that by the end the chemical treatments have weakened the paper fibres so that they abrade easily. Handle a washed salt print by its edges.

Stage 8 — Drying, the dry-down, and flattening

Blot or squeegee gently and air dry face up on a clean fibreglass or plastic screen, or on photographic blotters — Reilly’s method, and Bostick & Sullivan’s.

Expect the print to change again, and in your favour. Reilly: on drying, prints become more neutral in colour and gain slightly in density as the image layer contracts. Bostick & Sullivan: in the final drying stage the image will darken and the colour will richen even further, and there is a significant dry-down. Measure it.

📓The two numbers this session exists to produce

Both come from one step wedge printed alongside the picture.

The fix-down. Read a mid-tone patch, or count wedge steps, at three moments: out of the frame (dry, before any water), out of the fixer (blotted), and dry the next morning.

Δ_fix = D(out of frame) − D(dry, finished)

Fix-down, in density

steps lost = Δ_fix ÷ 0.15

The same in steps of a 21-step wedge

stops to add next time = (steps lost × 0.15) ÷ 0.30

And in exposure, which is what you will actually change

Photographers’ Formulary’s published expectation is the marked step plus about four more, which is 2.5 stops. Reilly’s is about two stops. If your figure is far outside two to three stops, something else is wrong — most likely the fixer strength, the fixing time, or a print that was not exposed deep enough to begin with.

The wet-to-dry shift. Read the same patch blotted-wet out of the final wash and again the next morning. That is a different quantity from the fix-down and it is what tells you how much of the darkening happens after the print looks finished. Mark the wet reading as indicative; a wet reflection density is not a measurement of the same surface.

And every number in this box is a method, not a result. The course has not run this session; your paper supplies the figures.

Flatten while slightly damp, not bone dry. Reilly’s instruction, with two warnings: it requires patience, and excessive pressure does not help. Acid-free blotters under weights, or a book press with silicone release paper against the coated side.

Heat is not neutral here. Reilly: using heat in drying or flattening may alter the appearance of some salted papers, especially plain ones — they turn colder in image colour and somewhat darker. That was a deliberate finishing step for Talbot, who went over his prints with a hot iron to intensify them, and it is a variable you should either use on purpose or exclude on purpose. Bostick & Sullivan recommend flattening in a warm dry mount press, which is exactly this effect being used.

And most salt prints should be matted rather than mounted. Reilly: because they are made on relatively heavy paper and carry little binder, most salted papers can simply be matted, and mounting should be employed only when necessary rather than as a matter of course. That is the opposite of the albumen convention, where the thin stock under a heavy albumen layer curls hard enough to tear itself and about 95 per cent of nineteenth-century prints were mounted. The gold and permanence lesson carries the adhesive and board rules if you must mount.

Stage 9 — Testing the print rather than assuming it

Two tests, both from Part XII, both run on your own sensitised, unexposed, identically processed strips rather than on the picture, and both with a caveat about the material.

Residual thiosulfate, with HT-2. Do this last, with the toner bottled and no acid on the bench, because the reagent contains acetic acid and this session has had a thiocyanate in it.

Residual silver, with ST-1, which is a sulfide reagent. Ventilation, separation from every acid, a drop on a test strip.

!Are these tests valid on a paper with no baryta layer?

Not established for the thiosulfate test, and this page says so rather than adapting it silently. Both tests were devised for gelatin-coated papers, where the reagent sits on a coating and the stain develops in it. On a salted paper the reagent soaks into cellulose, and no source read for this course reports a calibration of either test on an uncoated sheet. Treat a comparative result as meaningful — this strip against that strip, washed two different ways, on the same paper, on the same day — and treat an absolute reading against a printed comparison patch as unvalidated on this material.

The residual silver test is in a better position, and the evidence is historical. John Spiller detected residual silver in the whites of albumen prints in 1868 by exactly this chemistry: he moistened the white surface with ammonium sulfide and watched a brown stain appear, and that observation is what established that a fixer does not remove all the silver from these papers. The test’s chemistry is therefore known to work on a printed-out silver paper. What has not been established for a salted paper is the quantitative comparison.

And one thing the test will do that it does not do on a gelatin paper. A sulfide reagent on a nanoparticle silver image is a sulfiding agent, and the gold lesson shows what complete sulfiding costs: about thirty times the density. Keep it on the strip and off the picture, and never test in the image area “just to be sure”.

What a positive result means here. More than it would on a fibre-base paper, for the reason Reilly gives: there is no baryta layer between the residue and the image. A trace of thiosulfate in a gelatin print has a barrier to cross; in a salt print it is already in contact with 3 mg of the most vulnerable silver in the course. A positive result means rewash the print, not shrug.

And a non-destructive route exists for a finished print, though not for a home laboratory. The AIC’s Photographic Materials Group note that XRF identifies the silver image and can also detect sulfur where the image has been fixed in sodium thiosulfate, which is the professional version of this question.

Expected observations

In the frame. The margins darken first and fastest. Colour runs grey, red-brown, then purplish or brownish black; the deepest areas go greenish and lustrous as they bronze. The image looks distinctly, uncomfortably too dark when it is right.

In the first tray. A white milky cloud within seconds, thinning with each change. The print lightens by a shade or two and moves towards red.

In the toner. Shadows first. On a thiocyanate bath, a visible bleach before the intensification. The change is subtler and slower than you expect, and Bostick & Sullivan warn that on a paper with no gelatin it is also faster than on a gelatin printing-out paper, so watch rather than time.

In the fixer. The dramatic one. The rich purple or brown becomes a much yellower, duller brown, with a visible loss of density. This is normal and physical, and the chemistry lesson explains why: the silver chloride leaves, the refractive index falls and the particles pack together. The print should be about three quarters as dark as you want it when it comes out.

Overnight. It comes back. Darker, colder, richer. A print judged wet is judged wrong.

What is happening chemically

Four reactions, all developed in the two lessons this lab follows.

In the frame, photolysis with the excess silver nitrate recycling the halogen:

2 AgCl + light → 2 Ag + Cl₂

Light makes the image; nothing amplifies it

In the first tray, the excess silver nitrate meeting the ions in tap water:

AgNO₃ + NaCl → AgCl(s) + NaNO₃

The milky cloud: silver chloride precipitating in the wash water rather than in the print

In the toner, the displacement:

Ag + Au⁺ → Ag⁺ + Au

Gold(I): one silver atom leaves for each gold atom deposited

with the silver re-precipitating as silver chloride in the sheet, which is why fixing must follow.

And in the fixer, complexation — with the loss of density that comes from removing the silver chloride rather than from this reaction:

AgCl + 2 S₂O₃²⁻ → [Ag(S₂O₃)₂]³⁻ + Cl⁻

The unexposed chloride into the soluble bis(thiosulfato) complex

Data to record

Use the lab notebook and the exposure log.

Column	What goes in it
Print	Number; which sheet from the salting session, and its coating method
Paper and salting	Maker, product, weight; plain or citrate; batch numbers of both solutions
Silver	Bath strength and batch; float time or drop count; hours between sensitising and printing
Exposure	Source, distance and dose; or date, time, sky and orientation. Every inspection, with its time and the appearance
End point	What you saw when you stopped: bronzed margins, shadow appearance, fraction of final darkness
First wash	Number of changes, minutes, water temperature, when the cloud stopped
Toner	Which bath, strength, temperature, minutes, and the colour at the stop
Fixer	Which route, strength, one bath or two, minutes in each, temperature, and how many prints that bath had already taken
Wash	Minutes before the aid, minutes in the sulfite, minutes final, method and water temperature
D out of frame / D out of fixer / D dry	For a marked patch, or steps counted on a wedge
Δ fix-down, Δ wet-to-dry	Signed, in density and in stops
Stage 9	Both test results, the strips they were run on, and the wash regime each strip had

Analysis

First, decide what you may claim. One print per condition, hand coated, one paper, one session. Every conclusion takes the form “on this paper, with this fixer, on this day”.

Second, read the fix-down against the two published figures. Two to three stops is expected. Less than that suggests a fixer weaker or briefer than you thought, or a print that never reached maximum density. More suggests an over-strong or over-long fix — and Reilly’s warning about prolonged fixation applies to permanence as well as to density.

Third, lay the toned prints against the untoned control, dry, in daylight, and describe the difference in words before you describe it in numbers. Then measure maximum density on both. Reilly’s observation is that a gold toner also changes density, not only colour, and the direction depends on which account of the deposition is right — which the gold lesson says is genuinely unsettled. Your two prints are a data point on a question the literature has not closed.

Fourth, add the row to the comparison atlas. The same standard negative that gave Part XXI’s cyanotype row now gives a salted paper row: measured exposure scale, maximum density, image colour before and after toning, surface, and the conditions. That row is what the variants lesson asks you to complete, and what Part XXV’s atlas assignment closes.

And fifth, disposition Stage 9 honestly. A comparative test that shows one wash regime cleaner than another is a result. An absolute reading against a printed patch, on a paper the test was not calibrated for, is an indication.

Troubleshooting

What you see	Most likely cause	What to change
Print almost vanishes in the fixer	Under-exposed, or the fixer is too strong, too long, or acid	Check the fixer first — strength, time, and whether it is the bottle you meant. Then expose two to three stops deeper. The break/fix page separates the three from the record
Black stains appearing in the fixer	Free silver nitrate carried in: the first wash was too short	Wash until a trayful stays clear, not for a number of minutes
Toner does nothing at all	Free silver carried in from a short first wash; or an alkaline bath that has not ripened, is too alkaline, or is spent; or a trace of fixer in it	In that order. The gold lesson has the full diagnosis
Print bleaches on entering the toner and does not come back	If thiocyanate: it should come back — wait. If it does not, the bath is short of gold	Replenish: Bostick & Sullivan add 5 mL of gold stock per print, or 25 mL when toning slows
Flat, lifeless, reddish print after toning	An acidic gold(III) bath bleaching three silver atoms per gold	Check the bath is alkaline or properly complexed. This is Reilly’s description of exactly this failure
Red stains on the negative	Silver nitrate transferred from a damp sheet	The sheet must be dry, and use the 1 mil polyester spacer. Reilly’s precaution, for any negative you value
Doubled image around the edges, sharp centre	A cold frame put into sunlight; paper and negative expanded unequally	Let the frame reach the outdoor temperature before exposing
Milky white deposit dried onto the print	The first wash did not go to completion	More changes. It is silver chloride and it will not come off later
Print looks perfect wet and weak dry, or the reverse	You judged it wet	Every judgement — toning, density, colour — is made on a dry print against a dry reference
Highlights yellow within weeks	Residual silver or residual thiosulfate	Stage 9 on a strip from that session, then rewash. The break/fix page has the diagnosis
Paper fibres abrading in the final wash	Normal weakening from the chemical treatments	Handle by the edges. Photographers’ Formulary warn about it explicitly

Clean-up

Bottle the toner first, into its own labelled container, before anything else is moved. It is the one liquid in the room that must never meet an acid, and it is worth recovering for its gold as well as its silver.

Then the fixer, into the silver-bearing fixer bottle — a separate container from the first wash, because the silver in it is a thiosulfate complex and the silver in the wash water is a free ion.

Then the washes, first and intermediate, into the silver-bearing waste.

Rinse every tray into waste before it goes near the sink, and wash the trays that held silver separately from the trays that held toner. Wipe the bench while the residue is wet.

And put the frame away clean. Both faces of the glass, the pad, the back. A speck of dried silver nitrate on the glass prints as a mark on every subsequent sheet.

Storage

The finished print: flat, dry, matted rather than mounted where possible, and away from anything acidic. The gold and permanence lesson carries the enclosure, adhesive and environment rules, including the two published temperature and humidity ranges and why they differ.

The gold toner: the alkaline baths are mostly one-use and go inactive after a few hours with no warning; the acetate bath and the thiocyanate bath can be kept and replenished. Label with date, strength, and how many prints have been through it.

The fixer: make it fresh every session. Reilly is unambiguous — the extra silver present in these papers quickly exhausts a fixing bath, and even unused fixer solutions break down rapidly. His conservative capacity for maximum permanence is no more than 10 to 15 prints of about 8 × 10 inches per litre, against the literature’s estimate of up to 150 in a 15 per cent bath, and he prefers the conservative figure because the price of fixer is trivial next to everything else on the bench.

The washing aid: made in advance is fine, used once and discarded.

Disposal considerations

The chemistry. Four silver-bearing streams with three different silver chemistries: a free silver ion in the first wash, a gold-and-silver mixture in the toner, and silver-thiosulfate complexes in the fixer. The first can be precipitated with a chloride or a carbonate, which is how the trade recovered it; the third cannot, and is the stream Part XII’s silver recovery lesson deals with. Keep them separate for that reason as much as for safety.

The general practice is accumulation, labelling and recovery rather than disposal. Silver carries aquatic hazard statements and dilution is not a treatment. Gold is worth recovering on its own account.

The thiocyanate rule extends to the waste bottle, and it is the reason the toner has its own container: a thiocyanate waste and an acid waste in one bottle is the failure this page has been guarding against all evening.

And the caveat that is not a formality. The course publishes no jurisdiction-specific disposal instruction. Local regulation governs, it differs, and it is the only document that can answer the question for your drain. The disposal ruling says why.

Questions

1. Why must a salt print be exposed past the point where it looks right? Give the physical reason and two independent published figures for how far.
2. A print looks correct through the split back at eight minutes. Why keep exposing?
3. What is the white cloud in the first wash, and why is its disappearance a better end point than a time?
4. Give three separate reasons this fixer is not the fixer of Part XI — one about strength, one about pH, one about time.
5. Reilly asks for two fixing baths. Is that a safety margin or a chemical requirement? Answer in terms of what forms in an exhausted bath.
6. Why does a paper with no baryta layer wash differently from a fibre-base gelatin paper? Name the two effects that pull in opposite directions.
7. Your residual thiosulfate test on a salt print gives a faint stain. What can you conclude, and what can you not?
8. You measure a fix-down of 1.2 in density. How many stops is that, is it inside the expected range, and what would you change?

Further experiments

Three toning endpoints and an untoned control, from one negative, one coating session and one fixer. The single most informative afternoon in this part, and it produces the atlas row as a by-product.

Both fixer routes on one exposure. Cut a sensitised sheet in half, expose the halves together, process them identically except for the fixer — Reilly’s 15 per cent two-bath against the kit’s 5 per cent single bath — and read maximum density and the fix-down on both. Then run Stage 9 on strips from each. This is the experiment that settles the contested callout above for your paper, and neither source can settle it for you.

The wash-time series. Four identically fixed strips, washed 10, 20, 30 and 60 minutes with the same sulfite treatment, all tested for residual thiosulfate on the same day with the same reagent. Reilly says the evidence for these papers is almost nonexistent; this is the smallest experiment that adds any.

And the deliberate mistake, once, on a strip you do not care about. Fix a printed-out strip in the acid rapid fixer from your ordinary darkroom shelf, alongside a control in the plain bath. Do this only if there is no thiocyanate anywhere in the room, and read the acid rule at the top of this page again before you do. What you will see is Reilly’s excessive bleaching of the highlights and mid-tones, in about a minute, and you will not need to be told again.

Recap

The exposure is the development, so it is judged by looking — through a split back, indoors, with the margins as the guide and bronzing as the end point. Two to three stops past what looks right.

The first wash is worth four things: it saves the gold, prevents black stains, spares the fixer’s capacity and holds the recoverable silver. Its end point is a trayful of water that stays clear.

Tone before fixing, because toning makes silver chloride; wash between the two, because a toner in a fixer damages both; and judge the colour dry, against an untoned control, because everything you see in the tray is provisional.

The fixer is weak, brief, plain and alkaline, and each of those is a separate answer to a separate threat. Two baths, fresh every session, and never longer than the time.

No acid comes near this bench, and with a thiocyanate toner that rule is not about the print.

Wash, use the sulfite aid, wash again — and then test, because the wash times for these papers are extrapolated rather than measured, and the paper has no baryta layer to protect the image from what is left in it.

Check your understanding

Question 1. Why is a salt print exposed until it looks distinctly too dark?

• Because the paper continues to darken in the dark after exposure
• Because the fixer removes the silver chloride the image silver is dispersed in, which lowers the refractive index and packs the particles, so density and colour are lost before any silver has left
• Because the toner bleaches the image and the exposure has to allow for it
• Because the print is judged wet and wet prints always look darker

Show the answer and why

Answer: Because the fixer removes the silver chloride the image silver is dispersed in, which lowers the refractive index and packs the particles, so density and colour are lost before any silver has left

Reilly gives the mechanism as a physical one: in the unfixed print the image silver is dispersed almost as a solid solution in silver chloride, and removing the chloride lets the particles pack into aggregates while the refractive index of the layer falls, both of which reduce covering power. His overprinting figure for salted papers is about two stops; Photographers Formulary reach 2.5 stops by a different route, saying that the lightest step of a step table showing darkening, and usually four more, are lost in washing, toning and fixing. Some image silver is genuinely lost as well, particularly in an over-strong, over-long or acid bath - but the bulk of the change is the physics.

Question 2. What is the white milky cloud in the first wash?

• Image silver washing off the print
• Silver chloride and silver carbonate, precipitated in the tray as the excess silver nitrate in the sheet meets the chloride and carbonate ions in tap water
• Undissolved gelatin from the salting solution
• Silver sulfide from thiosulfate contamination

Show the answer and why

Answer: Silver chloride and silver carbonate, precipitated in the tray as the excess silver nitrate in the sheet meets the chloride and carbonate ions in tap water

Reilly identifies the reaction in his sensitising chapter, where he is explaining why the silver bath must be made with distilled water - tap water carries chloride and hard-water ions and silver nitrate meeting them throws down a cloudy precipitate - and then closes the loop by saying that the clouding of the water in the initial wash is that very reaction. That is why the end point is the cloud stopping rather than a time, and why Photographers Formulary specify a tray rather than running water: you need to be able to see it. It is also why this water is the stream the trade recovered its silver from.

Question 3. Reilly specifies two fixing baths of four minutes rather than one of eight. Why?

• To halve the concentration of silver in each bath and so extend capacity
• Because at least three silver-thiosulfate complexes form, thiosulfate must be in excess or insoluble complexes form that cannot be washed out, and one of those complexes is soluble only in fresh thiosulfate
• Because eight minutes in one bath would over-fix the print
• Because the first bath is used up by the toner carried in from the previous step

Show the answer and why

Answer: Because at least three silver-thiosulfate complexes form, thiosulfate must be in excess or insoluble complexes form that cannot be washed out, and one of those complexes is soluble only in fresh thiosulfate

It is a chemical requirement rather than a margin. Reilly sets out the reaction: the most important condition for effective fixation and for complete removal of the products is that thiosulfate ions be present in excess, or else insoluble complexes are formed which cannot be washed from the image layer, and one of the complexes formed during fixation is soluble only in fresh thiosulfate. The first bath does the bulk of the complexing and the second ensures that what is finally formed can be washed out - which matters more here than anywhere, because there is no baryta layer between the fibres and the image.

Question 4. Which of these are reasons the fixer for a printed-out paper is alkaline rather than acid?

• Slight alkalinity prevents any acid inadvertently introduced from decomposing the thiosulfate and liberating sulfur
• An acid fixing bath attacks the finely divided metallic silver of the image, bleaching the highlights and middletones
• Alkalinity speeds up the fixing reaction so the print spends less time in the bath
• An acid bath would dissolve the paper sizing

Show the answer and why

Answer: Slight alkalinity prevents any acid inadvertently introduced from decomposing the thiosulfate and liberating sulfur, An acid fixing bath attacks the finely divided metallic silver of the image, bleaching the highlights and middletones

Reilly gives exactly these two reasons for the 2 g of sodium carbonate in his 15 per cent bath, and both matter more on this material than on any other in the course. Free sulfur on nanoparticle silver is the sulfiding reaction that costs a salt print about thirty times its density, on Ware's extinction coefficients; and the attack on the image silver is amplified by the roughly hundredfold surface area of nanoparticle silver relative to the filamentary silver of a developed print. Alkalinity does not speed the reaction up, and the sizing is not the issue.

Question 5. You run the Part XII residual thiosulfate test on a salt print strip and get a faint stain. What may you conclude?

• Nothing at all: the test is invalid on this material
• That thiosulfate is present; but the test was devised for gelatin-coated papers and no source read for this course calibrates it on an uncoated sheet, so a comparative result between two of your own strips is meaningful and an absolute reading against a printed patch is not
• That the print is archivally washed, since the stain is faint
• That the print was under-fixed rather than under-washed

Show the answer and why

Answer: That thiosulfate is present; but the test was devised for gelatin-coated papers and no source read for this course calibrates it on an uncoated sheet, so a comparative result between two of your own strips is meaningful and an absolute reading against a printed patch is not

The distinction is the honest one and the page states it rather than adapting the test silently. On a gelatin paper the reagent sits on a coating; on a salted paper it soaks into cellulose, and the relationship between stain density and residual thiosulfate has not been established there. The residual silver test is in a better position because its chemistry is known to work on these papers - John Spiller detected residual silver in the whites of albumen prints in 1868 by moistening them with ammonium sulfide and watching a brown stain appear - but the quantitative comparison is equally uncalibrated. And a faint stain means rewash: there is no baryta layer between that residue and 3 mg of very vulnerable silver.

Question 6. Why does the toning step come before the fixing step?

• Because a fixed print will not take gold
• Because the toning reaction produces silver chloride as a by-product, which would re-sensitise a print that had already been fixed
• Because the fixer would dissolve the gold
• Because a wet print tones more evenly than a dry one

Show the answer and why

Answer: Because the toning reaction produces silver chloride as a by-product, which would re-sensitise a print that had already been fixed

Reilly gives the reason directly, and notes that toning after fixing works with equal success provided the print is fixed again afterwards. The toning displacement puts silver into solution, and in a sheet that still contains chloride that silver comes back down as silver chloride - light-sensitive material in a print that is supposed to be finished. The other rule in the same section is the one that catches people out in the opposite direction: the toner is ruined by even a trace of fixer, so the trays, the tongs and the hands that touch one must not touch the other.

Question 7. You have a print out of the frame at density 2.05 on a mid-tone patch and 0.85 on the same patch dry the next morning. What is the fix-down in stops, and what would you do?

• About 1.2 stops; expose about a stop more next time
• About 4 stops, which is far outside the expected two to three; suspect an over-strong, over-long or wrong fixer before changing the exposure
• About 2.5 stops, which is exactly as expected; change nothing
• The comparison is meaningless because the two readings are on different surfaces

Show the answer and why

Answer: About 4 stops, which is far outside the expected two to three; suspect an over-strong, over-long or wrong fixer before changing the exposure

A density difference of 1.20 divided by 0.30 is four stops, and both published expectations are lower: Reilly gives about two stops of overprinting for salted papers, and Photographers Formulary's "the marked step and usually four more" works out at 0.75 log H, which is 2.5 stops. A fix-down that large says the fixer took more than it should, so check its strength, its time and whether it was the bottle you intended before you start adding exposure. Exposing deeper to compensate for a fixer that is eating the print buys density at the cost of the permanence you were exposing deeply for in the first place.

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