Experiment: Selenium Toning and the Print Curve

Every source this part has read agrees that selenium toning raises maximum density and upper-scale contrast, and not one will tell you by how much on a paper you can buy. Kodak publish a curve for a paper they discontinued, in their developer. Moersch reports the effect and calls it “visible and measurable” without publishing a measurement. Getty describe it from the conservation side as “a slight increase in image contrast and brilliance”.

This session turns that adjective into a number. It costs one sheet each of three papers, one bath, and about two and a half hours, more than half of which is spent reading a densitometer.

Purpose

To measure what one stated selenium treatment does to the print curve of three papers that differ in image tone, and to establish which parts of that change are large enough to be real on your own instrument.

The hypothesis, in the form the measurement can refute: a selenium bath at one dilution and one time raises the maximum density and upper-scale slope of a developing-out silver gelatin print by an amount that depends on the paper’s emulsion, leaves the base and extreme highlights unchanged within measurement error, and shifts image hue most on the warm-tone paper and least on the cool-tone one. The directions come from three makers and a conservation atlas; the magnitudes come from nobody, which is why they are being measured.

The control is the untoned half of each sheet. Every sheet carries the same step wedge printed twice and is cut in half after processing, so the toned piece and its control were exposed under one wedge at one lamp setting, developed together, fixed in the same baths and washed in the same tray. It is not “an untoned print”; it is this print’s other half, and it goes through the whole session in a tray of plain water at the same temperature for the same four minutes.

The single variable is the toning treatment: selenium at 1+20 for four minutes at 20 °C, against plain water at the same temperature for the same time. Paper is not a variable but a block: the experiment runs three times over, once per paper, each compared only with itself. That is what makes three papers affordable, because two papers never have to agree about an absolute density, only about a difference.

!Why the control is wetted, when the manifest says the untoned half is kept dry

A print that is wetted and dried changes density. Part XVIII measured it and named it: the material component of dry-down is a small shift that survives drying. If the toned half is wetted and the control is not, every difference you measure is the toner plus a wetting cycle, and no arithmetic afterwards separates them.

So the control gets a sham treatment — the identical sequence with plain water in place of the toner — and “kept dry” is read as “kept out of the toner”, which it has to mean if the instruction to dry every piece by the same method is to make sense. That is this page’s design decision rather than a correction of a source, stated so a reader who disagrees can run it the other way.

Learning objectives

By the end you will be able to:

• design a within-sheet control for a treatment that cannot be reversed, and say why a separate control sheet would not do;
• expose a step wedge onto paper so the deepest step sits on the maximum black plateau, and predict how many of the twenty-one steps land on the curve rather than pinned at either end;
• run a selenium bath at a stated dilution, temperature and time with the endpoint set by the clock, and justify the clock where the printing pages tell you to use your eyes;
• read reflection density on a relative scale and say what such a scale can and cannot support — which is exactly what this experiment needs;
• plot two print curves and their difference on one pair of axes and read three numbers off them: the change in maximum density, the change in upper-scale slope, and the density at which the effect first clears your own noise;
• describe a hue change in a vocabulary a conservation source uses, state the limits of doing it by eye, and say what the session does not establish, including everything about permanence.

Prerequisites

• Selenium toning: selenosulfate, silver selenide and the protection claim — what is in the bottle, why the shadows move first, why dilution sets a rate rather than an endpoint, and the acid rule. This page assumes all of it and repeats none.
• Maximum black, base white and dry-down — finding the exposure that first reaches maximum black, and why every piece here is measured dry.
• Calibrating the densitometer — your three reflection repeatability figures, needed before the first reading.
• The step wedge exposure series — how a step number becomes a log exposure, and why an uncalibrated wedge gives a nominal scale.
• Paper emulsions, image tone and speed — why three papers present three different silver deposits.

Safety classification

Level B, an advanced home laboratory. The toner is bought as a liquid concentrate and diluted twenty-fold; nothing is weighed and nothing is heated. What keeps it above Level A is the concentrate and the discipline around it.

Which Level B criteria apply. Two of the rubric’s four. Handling of concentrated reagents toxic at the concentrations actually handled: HARMAN call their concentrate “a toxic chemical”, classify it Acute Tox. 4 with H302 and H317, and name sodium selenite at 1 to 5 per cent w/w; Moersch’s competing product is Acute Tox. 2, signal word Danger. A failure mode that is a splash of something that matters: 100 mL of concentrate is decanted into a graduate, and that is the most hazardous thirty seconds of the session.

Why not Level C. The makers do not ask for a fume cupboard: HARMAN ask for a well-ventilated area “preferably with some form of air extraction system”, and their safety data sheet offers “ventilation, local exhaust ventilation or breathing protection” as alternatives. The waste is collected, and a household’s lawful route to a collected hazardous stream in England and Wales is the local authority’s household waste and recycling centre. No chromium(VI) or formaldehyde is present.

The Level C operation this page does not contain. Kodak’s own selenium formulas begin by boiling elemental selenium powder in sulphite solution, and elemental selenium is Level D in this course. Nothing here is mixed from raw chemicals: the toner is a bought bottle whose composition its maker publishes only in a safety data sheet, which is why the formulary entries describe a product rather than a recipe.

⚠What is not a hazard here, and the conditions that would change that

Hydrogen selenide is not being generated in this room, and the rule against acid is absolute anyway. Princeton state that treating selenium salts with acid may release highly toxic hydrogen selenide; Moersch’s sheet records violent reaction with strong acids. Neither condition occurs here: the bath is alkaline — the one concentrate in this corpus that publishes a pH gives 9.53 — no acid is added, and the acid stop bath from the printing session is out of the room. HSE set dihydrogen selenide at 0.02 ppm over eight hours, a figure no darkroom can measure, which is why the control is a rule about bottles and trays rather than a threshold. What would change it: an acid stop bath decanted into the toner or its waste bottle, an acid tray cleaner on the toning dish, or selenium waste combined with acid waste.

Nothing is heated and nothing is weighed. The bath runs at 20 °C. The reason the sepia session in this part must route a Level C operation outside itself is that it weighs a deliquescent solid; this page weighs nothing, and the only airborne risk is a splash aerosol from careless pouring.

Silver is present but is not the session’s hazard. The pieces are fixed and washed; what silver remains is in the emulsion until the toner’s thiosulfate takes a little of it. That is a fact about the waste bottle’s label, not about the operator.

Hazards

Hazard	Where it arises	Control
Acute oral toxicity and skin sensitisation	Decanting 100 mL of concentrate	Gloves and eye protection before the cap is off; the graduate stands in a tray; no pouring at head height
Skin sensitisation on repeated contact	Four timed lifts out of the bath	Tongs, not fingers, on Kodak’s own instruction; change any glove contaminated inside
Eye damage from a splash	The lift-and-return step, where solution flies	Eye protection with side protection to EN ISO 16321-1, HARMAN’s own specification
Hydrogen selenide, if acid reaches the bath	The waste bottle, not the tray	Acid stop bath out of the room; a dedicated funnel; the selenium bottle shares with nothing
Aquatic toxicity	Every litre in the session	Collected; see Waste streams and Disposal
Inhalation of whatever the bath gives off	Four minutes over an open tray	General ventilation to the specification below, run throughout
A cut hand	Cutting three sheets in half	Steel rule and mat, blade away from the hand, done dry before any tray is filled

Required PPE

Nitrile gloves, single-use, from the moment the concentrate is opened until the last waste bottle is capped. HARMAN require rubber gloves “in all use and disposal”, and their safety data sheet specifies impervious gloves to EN 374; read glove selection before substituting.

Eye protection with side protection to EN ISO 16321-1, HARMAN’s own specification: splash goggles for decanting, spectacles with side shields acceptable once the bath is in the tray. An apron, which HARMAN ask for by name alongside gloves and glasses.

A respirator is not part of this page’s control, and the reason belongs on the page rather than in a gap. HARMAN’s sheet says a filter type A mask “may be appropriate”; type A filters are for organic vapours, and no source read establishes what a working selenium bath puts into the air. A mask chosen against an unidentified contaminant is a guess wearing a certification number, so the control is dilution of the air, run continuously.

Ventilation

What the makers ask for. HARMAN “strongly recommend” a well-ventilated area, “preferably with some form of air extraction system”; their safety data sheet asks for ventilation, local exhaust ventilation or breathing protection. Princeton are firmer: toning solutions must be used with local exhaust ventilation.

What this page requires. HSE’s COSHH essentials sheet for manual film and plate development specifies a good standard of general ventilation from powered wall- or window-mounted fans, greater than five air changes per hour, with a through draught, plus easy-to-clean lipped surfaces and shallow trays. Run the ventilation check before the session; a fan switched on when the tray starts to smell is too late.

The gap between the two is real. Local exhaust captures at source; general ventilation dilutes after the fact. This page runs on the weaker control and compensates by keeping the exposure short: one tray, four minutes of open bath, bottled the moment the last piece leaves it.

Materials

Item	Quantity	Note
ILFORD MULTIGRADE RC DELUXE, glossy, 8 × 10 in	3 sheets	The neutral block; ILFORD’s range table gives it a cool/neutral image tone
ILFORD MULTIGRADE RC WARMTONE, glossy, 8 × 10 in	3 sheets	The warm block, 190 g/m². Where the makers predict the largest change
ILFORD MULTIGRADE RC COOLTONE, glossy, 8 × 10 in	3 sheets	The cool block, 190 g/m². Where they predict the smallest
21-step transmission step wedge	1	A Stouffer T2115 or equivalent: 21 steps of a nominal 0.15 to a maximum density of 3.05, on a piece 12.7 × 127 mm
Clean plate glass, about 200 × 250 mm, edges taped	1	Holds the wedge in contact with the paper
Card mask with two windows, 8 × 10 in	1	Registers the wedge in the same two positions on every sheet
Self-healing mat, steel rule, sharp knife	1 each	The cut is made dry and once
Tap water	about 20 L	Rewetting, sham bath, two stop-bath changes and two washes; the course’s own arithmetic from the volumes below
Waste containers, 5 L and 15 L, labelled, screw-capped	2	Selenium-bearing and wash water
Storage bottle for the working toner, 2.5 L, opaque	1	HARMAN give a working solution six months in a full capped bottle and seven days in an open tray

Glossy on all three, deliberately. ILFORD state that MULTIGRADE FB CLASSIC’s glossy 1K surface “responds more favourably to toning than the matt 5K surface”, and surface is one of the four factors Kodak name as governing a toner’s visual effect. Holding it constant is the point of a blocked design; taking the more responsive surface gives the effect a chance to clear your noise floor.

Chemicals

Chemical	Quantity	Form
Selenium toner concentrate — HARMAN or Kodak Rapid Selenium Toner	100 mL	Bought liquid concentrate. Record maker, product and lot: HARMAN name sodium selenite, Moersch names sodium selenate, Kodak name neither
Water for the working bath	2.0 L	Making 2.1 L at 1+20
Ammonium thiosulfate rapid fixer concentrate	60 mL	1+4, as two baths of 150 mL for rewetting. Non-hardening
Paper developer concentrate	100 mL	1+9 to make 1 L, for the printing session
Citric acid stop bath concentrate	30 mL	1+19 to make 600 mL, printing session only. It does not enter the toning room
Wetting agent	5 mL	1+200 final rinse, ILFORD’s own instruction for even drying

Bath	Made from	Strength
Selenium toner, 2.1 L	100 mL of concentrate into 2.0 L of water	1+20, one part concentrate to twenty parts water
Sham bath, 2.1 L	Plain water at the toner’s temperature	The control’s tray
Stop bath	Plain water, changed between papers	Moersch: clearing agents are not stop baths for selenium toners

!Why 1+20 and four minutes, when the published range runs from 1+3 to 1+400

1+20 is the only dilution both makers publish, and both attach the same purpose to it. Kodak give 1:20 for print protection and 1:20 or 1:40 “to increase shadow contrast and maximum density with a minimum tone change”; HARMAN give 1+20 “where the primary reason is for protection of the image, with minimal tone change”. Two independent products, one number, one stated intention.

Four minutes sits inside both windows. Kodak put complete toning at 2 to 8 minutes at 20 °C depending on paper type and weight; HARMAN say protection at 1+20 “will be complete in 2–4 minutes”. Four is the largest number inside both, and it is also the toning time under Kodak’s published POLYMAX curve — which makes their figure a comparison of shape, though their dilution was 1:40 and their paper is discontinued.

And four minutes is what the resin-coated wet-time budget will pay for. ILFORD state that wet times beyond fifteen minutes risk edge penetration and curl on resin-coated paper; Kodak add that toning one longer than 8 to 10 minutes calls for a large border to trim off. Eight minutes of toning does not fit inside the budget under Procedure; four does.

One notation caution: Kodak write 1:20 and never define it, while HARMAN and Moersch write 1+20, one part plus twenty. This course treats them as the same, an assumption flagged as one on the chemistry page.

Equipment

An enlarger with a working timer, and a safelight the paper is cleared for: two exposures on one sheet double the time it spends under that lamp.

Five dishes of 12 × 16 in in plastic or unchipped enamel: toner, sham, stop, wash, spare. Kodak’s instruction is unqualified, no metal trays or tanks for toning solutions. The size is specified because three half-sheets of 203 × 127 mm lie side by side in one without overlapping, and pieces that overlap are toned unevenly. Two pairs of print tongs, one for the toner and one for everything else, never swapped. A 100 mL and a 2 L graduate, a funnel dedicated to the toner, a thermometer good to 0.5 °C, a timer and a squeegee.

A densitometer with a 45/0 reflection head — Part XV’s, built at stage 7, or a borrowed instrument. This is the one thing the experiment cannot run without. A drying rack, and a viewing lamp whose type you can write down.

Estimated cost

Band ££. The capital — a densitometer with a reflection head, and a step wedge — is required by earlier parts. What this session adds to the shelf is a bottle of selenium toner and two boxes of paper. The planner holds the dated figures and, more usefully here, the gaps: it prices the toner now, but neither of the two toned papers, and not the step wedge.

Estimated consumables cost

Every figure with a source is the planner’s own dated UK price and every quantity comes from the tables above. Two rows carry no number.

Consumed	This session	Sourced price	Cost this session
MULTIGRADE RC DELUXE, 8 × 10 in	3 sheets	£33.50 for 25 to £96.18 for 100	£2.88 to £4.02
MULTIGRADE RC WARMTONE, 8 × 10 in	3 sheets	The price file could not price it, and it is not among the gaps the file names: this page names a new one	—
MULTIGRADE RC COOLTONE, 8 × 10 in	3 sheets	The price file could not price it either: a second new one	—
Selenium toner concentrate	100 mL	£21.95 per 946 mL of Kodak rapid selenium toner, checked 7 September 2026	£2.32
Paper developer concentrate	100 mL	£10.52 per 500 mL to £20.03 per 1 L	£2.00 to £2.10
Stop bath concentrate	30 mL	£10.66 to £12.18 per 500 mL	£0.64 to £0.73
Rapid fixer concentrate	60 mL, as two baths	£21.05 to £25.98 per 1 L	£1.26 to £1.56
Wetting agent	5 mL	£28.70 per 1 L of concentrate	£0.14

The priced rows come to about £9.25 to £10.90 for one run, and that is a floor and not a total: two of the eight consumables have no sourced price, and both are peculiar to this page.

Outside the table, because the price file does not hold them, three observations from one British retailer on 6 September 2026, given as magnitudes: Ilford Selenium Toner 1 L at £51.52, MULTIGRADE Warmtone RC glossy 8 × 10 in at £37.42 for 25 sheets, and Cooltone RC glossy at £35.58 for 25. The Kodak bottle that was the fourth of them is now a record in the file and carries the toner row above; on the Ilford bottle instead, 100 mL of concentrate would be about £5.15 a run against the £2.32 the table shows. The paper is the real cost, and it is a cost of stocking three papers rather than of running this session.

Equipment is deliberately absent: a densitometer, a step wedge, five dishes and tongs are not consumed, and a page that counts them has stopped measuring what the calculator needs.

Waste streams

Two streams, two containers, and the larger one is water.

• Selenium-bearing: the two stop-bath changes, about 4.2 L, plus the 2.1 L bath itself if it is discarded rather than bottled. Kodak’s guidance for amateurs lists what a domestic photographer may send to the sewer, then lists what may not, selenium toners first; in their table of routes, used Rapid Selenium Toner is the only product with every route withheld but household hazardous waste collection.
• Wash and sham water, about 14 L on the course’s own arithmetic from the volumes above. The sham bath and the rewetting wash never met the toner; the final wash carries whatever the prints still held after two stop-bath changes. All of it is collected, because the disposal ruling reads separately collected home photochemistry as an absolute hazardous entry in the List of Waste, and WM3 is explicit that such an entry applies even where the waste displays no hazardous property. Kodak would allow wash waters to the sewer; the course records the disagreement and follows the stricter. Fourteen litres is the largest volume in this part and the best reason to plan the session once and run it once.

Keep the bath rather than discard it. HARMAN give a working solution six months in a full capped bottle against seven days in an open tray, so bottling the 2.1 L turns the largest hazardous stream into stock for the Further experiments. Label it with the date, the dilution and what it has toned, because HARMAN also state that the rate of tonal change slows as a solution ages — an aged bath is a different bath.

The two small rewetting fixer baths go to the silver-bearing waste container.

Alternative route

The session needs a darkroom for the printing and a reflection densitometer for the reading. Those are two problems with two answers.

Without a darkroom, borrow one for twenty minutes. Only the Preparation is dark work: three sheets, two exposures each, one developer. What cannot be delegated is the design, so give whoever makes the sheets the Preparation section entire — the two-window mask, the identical exposures, the two-bath non-hardening fix and the full wash are the experiment.

Without a reflection densitometer there is no substitute that preserves the result, and the honest thing is to say which half survives. The quantity here is a difference of about 0.02 to 0.25, and the eye is a poor comparator at the shadow end where it lives. The hue observation works unchanged: two pieces under one light is what the eye does well and a densitometer cannot do at all. The direction and ranking survive. The three numbers do not — a ΔDmax of 0.10 is invisible between two glossy blacks in a dish.

With a transmission head but no reflection one, the attachment is stage 7 of the optical head build.

Where selenium cannot be run at all — no extraction, no through draught, no hazardous waste route — the answer is not to move outdoors as a first resort. Outdoor working is the sulfide session’s route because sulfide’s hazard is a gas that disperses; selenium’s governing hazard is aquatic, and a tray outdoors is one spill from the ground. If the waste route does not exist, the session does not happen. What replaces it is the sepia experiment, which measures the same kind of thing in the opposite direction, and the permanence lesson.

Preparation

Before the day: the wedge and the mask

Cut a card mask the size of a sheet, 203 × 254 mm, with two rectangular windows a little larger than the wedge, their long axes parallel to the short edge, centred 63 mm and 190 mm from one end. Mark them T and C and cut a registration notch in the leading corner. The mask puts the wedge in the same two places on every sheet, shields the half not being exposed, and its notch tells you afterwards which half was T.

The 127 mm cut line falls between the windows, leaving each scale about 50 mm clear of it. That margin is not decorative: Kodak warn that toner penetrates the edges of resin-coated paper, and a knife cut through the resin layer opens the paper core to the bath.

One sheet, two identical scales, one cut

1. 1Two exposures through one wedge — same lamp, same aperture, same time, made back to back
2. 2Step 1 is the darkest patch — the clearest step of the wedge passes the most light, and it is the one that must reach maximum black
3. 3The cut line, 127 mm from the bottom edge — made dry, against a steel rule, before any tray is filled
4. 4The registration notch — the only thing that tells you which piece was T once both are dry and nearly identical
5. 5Two trays, one difference — the control is not left out; it is given everything except the selenium

The layout is the course's own. The margin at the cut answers Kodak's warning about toner entering the edges of resin-coated paper, and the two-scales-on-one-sheet arrangement is what makes the control a half of the same print.

The printing session

1. Warm the enlarger lamp for five minutes and leave it on throughout. Two exposures on one sheet are identical only if the lamp is.
2. Find the exposure that puts step 1 on the maximum-black plateau, per paper, by Part XVIII’s method: a bracket in thirds of a stop, developed to the paper’s own time, read dry. Take the first exposure at which step 1 stops getting darker and add a third of a stop. The three papers will not agree — ILFORD publish different relative exposures for each — and they need not, because no comparison here crosses papers.
3. Expose unfiltered and write that down. Filtration changes the curve’s slope; what matters is that it is identical for both halves of one sheet, which it is by construction.
4. Expose window T, then window C, the mask shielding the other, at the same time and aperture, the wedge emulsion-side down under glass in both positions. Do not move the head between them.
5. Develop in MULTIGRADE developer at 1+9 for 1 minute at 20 °C, ILFORD’s figure for their resin-coated papers, agitating continuously. Not less: ILFORD state that prints developed for shorter times may be underdeveloped and lacking in contrast and density, and an underdeveloped print is one whose maximum black you never reached.
6. Stop in ILFOSTOP at 1+19 for 10 seconds.
7. Fix in two baths of non-hardening rapid fixer at 1+4, 30 seconds each. Kodak’s guidance for prints to be toned is two-bath, non-hardening fixing; ILFORD note that a hardening fixer reduces washing efficiency. Do not extend it. Kodak state that prolonged fixing lets solution into the base and makes selenium- and sulfide-toned prints turn yellow, and can reduce the silver image; ILFORD add that long fixing affects image colour — here, a systematic error dressed as a result.
8. Wash 4 minutes in running water, Kodak’s figure for resin-coated paper before toning and longer than ILFORD’s 2-minute processing figure. Kodak’s reason is that thorough washing matters especially before toning, residual silver salts and traces of hypo causing stains, uneven tones and fading.
9. Squeegee, rinse in wetting agent at 1+200, air-dry at room temperature. No heat: Kodak record that heat drying shifts some paper and toner combinations to a cooler tone.
10. Cut each sheet in half along the 127 mm line, dry, one pass against the steel rule. Pencil the back of every piece: paper, T or C, date.

Three ways the halves stop being identical, all in this session. The lamp drifted — warm it, and make T and C back to back. Something changed the illumination — a wedge a millimetre out in the second window does not matter, but moving the head or touching the aperture does. The dish was crowded — develop one sheet at a time.

Procedure

Five stages. Stages 1 and 5 are reading, and between them they take longer than everything else.

Stage 1 — Read every step, before anything (about 25 minutes)

Anchor the reflection head on its white tile and black trap, and write your three reflection repeatability figures — untouched, sample replaced, head refitted — at the top of the log before the first reading. Those decide what counts as a result.

Read all twenty-one steps on all six pieces, dry, in one room at one temperature, each flat against the port: 126 readings, about twenty-five minutes with a helper writing. Work in a fixed order and never lift a piece off the port to re-check a reading, because re-seating the sample is the largest of the three repeatability terms.

What this pass is for. It is not the “before” of a before-and-after. It is the check that T and C were ever the same print. Subtract C from T at every step: the residuals should scatter about zero at the size of your replaced-sample figure. If they show a trend, one half denser than the other across the whole scale, the two exposures were not equal, and everything downstream is corrected by that difference rather than compared against zero.

Expect only seven to nine steps on the curve. A T2115 spans 3.00 in log exposure against a paper’s exposure scale of nearer 1.0 to 1.2, so the print divides into a run pinned at maximum black, a run at base white, and the working steps between. Read all twenty-one anyway: the pinned shadow steps are where the selenium effect is largest, and because they are pinned they move together, so a shift repeated across five adjacent steps is a shift while a shift at one step is a reading.

Stage 2 — The bench, and the order the trays are filled (about 20 minutes)

Ventilation on and checked. The acid stop bath from the printing session out of the room. Five dishes laid out with the lights on: sham, toner, stop, wash, spare.

Fill the sham and stop dishes with plain water and let them reach room temperature. Then put on gloves and eye protection, stand the graduate in the spare dish, measure 100 mL of concentrate into it, and add that to the 2.0 L of water rather than the other way round.

Bring both baths to 20 °C ± 1, HARMAN’s nominal working temperature and Kodak’s stated figure. HARMAN put their plain-water dishes about 4 °C warmer than the toner; here the sham bath is a control rather than a holding tray, so it matches. Record the temperatures achieved, not the ones intended.

Stage 3 — Rewet, and the four-minute run (about 10 minutes)

Rewet all six pieces together, T and C alike: 30 seconds in each of two fresh baths of rapid fixer at 1+4, then 4 minutes of running water — Kodak’s instruction for already-dried prints in the Rapid Selenium Toner procedure.

⁇Kodak give two instructions for rewetting a dry print, one page apart

The general Toning section of G-23 says a print already dry is soaked in water for two to three minutes. The Rapid Selenium Toner procedure on the next page says prints already dried are rewetted by immersion in a fixing bath and then rewashed, “otherwise staining may occur”.

Both are Kodak’s, in one document, about one operation. The course takes the second: it is the specific instruction for this toner rather than the general one for all of them, and it is the more demanding, so following it cannot cause the failure the other warns about. It costs about two more minutes of the wet budget than a water soak would, and removes a failure mode the page cannot afford, since a stain in a measured patch cannot be salvaged. The disagreement is recorded rather than resolved; the course has no measurement either way.

Then, with the timer running:

1. t = 0. Slide the three T pieces into the toner, face up, and the three C pieces into the sham bath. Rock both dishes gently and continuously for the whole four minutes. Do not watch the prints in the toner: HARMAN’s instruction is that continual observation makes subtle changes harder to see.
2. Four lifts, at 30 s, 1 min, 2 min and 4 min. At each, lift a T piece with the toner tongs, drain it five seconds, lay it beside its own C piece under the viewing lamp, look for eight seconds, write a word, return it; then the next paper. Keep the cycle under forty seconds and record the immersed time actually achieved, because time out of the bath comes off the four minutes.
3. At 4 minutes, out into the plain-water stop dish: 40 seconds of agitation, HARMAN’s figure for stopping the action, then a fresh change of water and another 40 seconds.

Kodak’s “pull it before it looks right” is already handled. They state that toning continues to some extent in the wash, which is why their procedure removes the print at almost the required tone. With a stated time as the endpoint, the answer is not to shorten the four minutes but to make the stop and the wash identical for every piece, so whatever continues, continues equally: a variable you cannot eliminate can still be held constant.

!The one place this page overrules the printing pages: use the clock

Every printing page in Parts XVIII and XIX tells you to judge by eye against a reference, and HARMAN’s sheet says the same. This page says four minutes on a timer.

In a printing session the endpoint is an appearance, so the eye is the right instrument. Here the treatment is the independent variable, and a variable set by how something looks is not independent at all: it is a second measurement made by the least repeatable instrument in the room, and it would make the three papers incomparable in exactly the way the blocked design exists to prevent. The lifts are still visual, but they record the trajectory rather than deciding the endpoint.

Stage 4 — Wash and dry, identically (about 25 minutes)

Wash all six pieces together in 4 minutes of running water, Kodak’s figure after toning a resin-coated print. HARMAN publish 2 minutes; the longer figure is taken because it is also Kodak’s figure before toning, and one number for both is one fewer thing to get wrong.

Squeegee both sides, rinse in wetting agent at 1+200, and air-dry at room temperature on a rack, no heat, all six laid out at once so they dry in the same air. A dryer used on the T pieces and not the C pieces would put Kodak’s cooler-tone shift straight into the result. Resin-coated paper dries in 10 to 20 minutes.

Close the wet-time budget in the log.

Step	Wet minutes	Running total
Rewet: two fixer baths	1.0	1.0
Rewet: wash	4.0	5.0
Toner or sham	4.0	9.0
Stop, two changes	1.3	10.3
Final wash	4.0	14.3

Under ILFORD’s fifteen-minute ceiling, and only just. If your times ran over, say so, and check every cut edge before trusting the outermost patches.

Stage 5 — Read every step again, and read the hue (about 35 minutes)

Wait until every piece has been dry thirty minutes. Re-anchor on the tile and the trap — a new session of the instrument, so head-refitted repeatability applies — and read all twenty-one steps on all six pieces again, in the order of stage 1.

Then, with all six dry, the hue reading. One light source, named: its type, its stated colour temperature if the maker gives one, and whether daylight was on the bench; never two lights. The reference is the C piece of the same paper, laid edge to edge with its T piece so the scales line up step for step, never a different paper. Look three to five steps up from maximum black, where Moersch reports the split appearing first, rather than at the black itself where every paper looks much the same.

Use the conservation literature’s vocabulary rather than inventing a scale. Getty call fully selenium-toned silver gelatin dark brown-orange, and archival selenium toning a treatment with no major colour change and “a slight increase in image contrast and brilliance”. The AIC catalogue calls untoned developing-out prints blue-black, and the printing-out range warm browns to cool purples. Kodak’s range for this toner is cool chocolate-brown, purplish brown, or no change. A hue outside those terms is described by naming the two it sits between.

🔬What the eye can and cannot report, and the instrument that would settle it

The eye is an excellent comparator and a poor meter. Two pieces edge to edge under one light show a hue difference far below anything you could name in isolation, which is why C is laid against T rather than remembered. What the eye cannot give is a magnitude, or a number another reader could reproduce.

A spectrophotometer would, in CIELAB coordinates and a colour difference. The course specifies none, the planner prices none, and this page will not pretend a phone camera is one.

The course’s own instrument sits between the two. ISO 5-3 records that a density is fully defined only by giving both its geometric and its spectral conditions, spectral response being the product of the detector’s sensitivity and every filter in the path. Part XV’s reflection head carries two matched green LEDs, so every density here is a green-channel density and not a status density. Fit a matched pair of blue LEDs as well, read one shadow patch in green and again in blue, and the difference between the two channels is a reproducible, instrument-defined number that moves when the hue moves. It is a colour signal defined by your own instrument, not a colour measurement, and saying so is the honest form.

Getty close the point from the other end: selenium is detectable by X-ray fluorescence “even in photographs toned for a very short period of time”, including where the toning cannot be seen at all. The instrument that reliably detects selenium toning was never a colour instrument.

Expected observations

On the neutral paper, a small rise concentrated in the deepest steps, quite possibly at the edge of what your instrument resolves, and a hue change you would not notice without the C piece beside it. Kodak’s own table entry for this toner at this dilution reads, flatly, No Tone Shift.

On the warm-tone paper, the largest of the three effects on both counts: warm-tone papers “usually produce the most visible effects” (HARMAN), “cool chocolate-brown hues” (Kodak), “tones quickly with a clear change in image colour” (Moersch). Expect the hue change to be obvious by the two-minute lift.

On the cool-tone paper, the smallest, possibly nothing visible. Kodak: “very little or no change with cold-tone papers”. Moersch: the alteration “is often barely visible even in a strong solution for a longer duration”. ILFORD recommend selenium for their cool papers because it leaves their image colour alone. A null hue result here is the predicted result, not a failed session.

In the lifts, the change well advanced by two minutes and nearly finished by four, because both makers’ windows say so. In the difference curve, a rise from about zero at base white to a maximum at the shadow end, flattening across the steps already pinned at maximum black. A negative difference above the toe is an error before it is a discovery: the one published account of selenium costing density is Moersch’s note that shadow density can fall before a very dilute bath reaches the highlights, and that is a matter of a long bath rather than of four minutes.

A change at base white would surprise everyone. There is no image silver there to convert, so a base-white difference above your repeatability is a stain, a wetting artefact or instrument drift — the single most useful diagnostic on the sheet.

What is happening chemically

The bath holds a soluble selenium salt, a thiosulfate and a sulfite — two makers’ composition tables plus the course’s inference about the three functional slots, not anybody’s statement of a mechanism. Kodak state the outcome and nothing between: the toner “converts the silver image to silver selenide”.

Why density rises rather than falls. This toner and a sulfide toner both replace metallic silver with a compound of silver and move density in opposite directions, so the direction is a property of the compound rather than of the operation. For sulfide the course can argue it numerically, because Ware publishes extinction coefficients for nanoparticle silver and silver sulfide. For selenide it cannot. No source in this corpus gives an extinction coefficient, a solubility product or a balanced equation for the formation of silver selenide from image silver, and the course prints none. The rise in maximum density is an observed effect — Kodak’s curve, Moersch’s report, and after this session your own table — from which a higher covering power is inferred. Keeping that order straight matters, because an inference like this hardens into a fact if nobody records which way round it was derived.

Why the effect is concentrated in the shadows. Moersch states it as a rule holding irrespective of dilution or temperature: the toner always reaches the higher densities first. Nobody read explains why, the surface-area argument points the other way, and the chemistry page sets the disagreement out. This session makes it measurable rather than arguable: the difference curve you plot is the shape of that claim.

Why the conversion is partial. Moersch bleached a print toned six minutes at 1+10 and found silver still unconverted; four minutes at 1+20 is weaker than that. What you measure is the density change from converting some of the silver, mostly where it is thickest, and it does not extrapolate: doubling the time will not double it, because the reaction runs out of accessible silver rather than out of clock.

Why the thiosulfate matters to the experiment and not only to the waste bottle. Every selenium toner Moersch knows of contains thiosulphate, a silver solvent, so the bath can take a little silver out of a print — a density loss running against the selenide’s gain. On a fully fixed, washed print in four minutes it is small; on a badly fixed one it is not, and it arrives uneven and stained. That is why Preparation insists on two-bath fixing and a full wash, and why an unexplained negative difference is a processing fault first.

Data to record

Two records: a session log written once, and a measurement table with one row per step per piece.

The session log

Date, room temperature, and the ventilation arrangement actually running. Paper, for each of the three: maker, product, surface, weight, size, box or batch code. Wedge: maker, part number, serial if it has one, and whether it is calibrated — a plain T2115 is manufactured to the increment and not certified to it, so every log exposure below is nominal.

Printing: enlarger, lens, aperture, height, filtration, exposure per paper and the bracket it came from; developer, dilution, temperature, time, agitation; stop bath and time; fixer product, dilution, time in each bath and the running total; wash time; drying method.

Toning: maker, product, lot number, the sheet’s document date, dilution as the sheet writes it and as you made it, volumes of concentrate and water, bath temperature at t = 0 and t = 4, sham bath temperature, immersed time achieved for each piece, the four lift times, stop-bath changes, wash time, drying method and time.

Instrument: densitometer, head, aperture, LED dominant wavelength and half-width from its datasheet, date of last calibration, reflection ceiling, all three reflection repeatability figures, and whether the head was refitted between passes, because that decides which applies. Viewing: the lamp, its type and stated colour temperature, and whether daylight reached the bench.

The measurement table

Column	What goes in it
Paper	Deluxe, Warmtone, Cooltone
Piece	T or C
Pass	1 (before) or 2 (after)
Step	1 to 21
Nominal wedge density	0.05 + 0.15 × (step − 1)
Reflection density	The reading, on your relative scale
Flag	Pinned at Dmax, pinned at base, or on the slope

The one number that is not in the table

Your noise floor, from pass 1: the largest absolute T − C residual before anything happened. Write it at the top of the analysis rather than the bottom, because it decides which numbers below are results.

Analysis

First, fix what you may claim. If the pass 1 residuals scatter about zero at the size of your repeatability, subtract nothing and use that repeatability as the threshold. If they show an offset or a trend, subtract the pass 1 residual step by step from the pass 2 residual and say so: you are measuring the toner against a pair of prints that were not identical, and the correction is the honest repair.

Second, plot the pair and the difference on one pair of axes, reflection density against nominal relative log exposure, with T − C beneath on the same scale. Follow Kodak’s sensitometry workbook and make the scales equal, so 0.30 of density is the same length as 0.30 of log exposure; a curve on unequal scales has a slope you cannot read.

The shape to expect, and why the difference gets its own curve

• Control half (untoned)
• Toned half, selenium 1+20, four minutes
• The difference, toned minus control

Show the numbers behind this plot

Three curves on one pair of axes, with relative log exposure increasing to the right so that the darkest patches lie at the right-hand end. The untoned control curve, drawn solid, leaves a base density of about 0.07 and runs flat until a log exposure of about 0.9, then rises steeply through 0.36 at 1.2 and 1.20 at 1.8, and shoulders over to a maximum of about 2.11 by log exposure 2.7, staying flat to the right-hand edge. The toned curve, drawn dashed, is indistinguishable from the control through the base and the toe, separates visibly above a log exposure of about 1.2, and finishes higher, shouldering to a maximum of about 2.32. The two curves therefore share a toe and diverge in the upper scale, the gap widening as density increases. Along the bottom of the plot a third curve, dotted, is the difference between them: it sits on zero from the left-hand edge to about log exposure 0.9, lifts to 0.03 at 1.2, rises through 0.11 at 1.8 and 0.16 at 2.1, and flattens at about 0.21 across the region where both curves have reached their maximum density. A horizontal guide line is drawn at a difference of 0.03, labelled as a typical noise floor, and the difference curve crosses it near a log exposure of 1.2.

Series	Nominal relative log exposure	Reflection density
Control half (untoned)	0.00	0.07
Control half (untoned)	0.30	0.07
Control half (untoned)	0.60	0.09
Control half (untoned)	0.90	0.16
Control half (untoned)	1.20	0.36
Control half (untoned)	1.50	0.72
Control half (untoned)	1.80	1.20
Control half (untoned)	2.10	1.70
Control half (untoned)	2.40	2.02
Control half (untoned)	2.70	2.10
Control half (untoned)	3.00	2.11
Toned half, selenium 1+20, four minutes	0.00	0.07
Toned half, selenium 1+20, four minutes	0.30	0.07
Toned half, selenium 1+20, four minutes	0.60	0.09
Toned half, selenium 1+20, four minutes	0.90	0.17
Toned half, selenium 1+20, four minutes	1.20	0.39
Toned half, selenium 1+20, four minutes	1.50	0.78
Toned half, selenium 1+20, four minutes	1.80	1.31
Toned half, selenium 1+20, four minutes	2.10	1.86
Toned half, selenium 1+20, four minutes	2.40	2.22
Toned half, selenium 1+20, four minutes	2.70	2.31
Toned half, selenium 1+20, four minutes	3.00	2.32
The difference, toned minus control	0.00	0.00
The difference, toned minus control	0.30	0.00
The difference, toned minus control	0.60	0.00
The difference, toned minus control	0.90	0.01
The difference, toned minus control	1.20	0.03
The difference, toned minus control	1.50	0.06
The difference, toned minus control	1.80	0.11
The difference, toned minus control	2.10	0.16
The difference, toned minus control	2.40	0.20
The difference, toned minus control	2.70	0.21
The difference, toned minus control	3.00	0.21

Constructed to show the shape and the reading, not measured. No source in this course's corpus publishes numerical print-curve data for a selenium-toned paper: Kodak publish their POLYMAX curve as a picture rather than as numbers, and the numbers that belong on these axes are the ones you measure. Read three features — the shared toe, the divergence in the upper scale, and the plateau in the difference across the steps already at maximum black. The curve is drawn to show the shape, not measured from a real material. Your own materials will differ, and measuring them is what the sensitometry part of the course is for.

🧮The three numbers, worked on constructed figures

Every number in this box is invented to demonstrate the method. None is a measurement, and none should be copied into a notebook. The course has not run this session and publishes no data from it.

Suppose your replaced-sample repeatability is 0.015 and the pass 1 residuals scatter within ±0.02 with no trend. Take 0.03 as the threshold, twice the repeatability, which is Part XV’s convention.

Maximum density. Five steps are flagged as pinned at maximum black. Their pass 2 T − C values are 0.19, 0.22, 0.21, 0.20 and 0.23, mean 0.21; their pass 1 residuals averaged 0.01. So

ΔD_max = 0.21 − 0.01 = 0.20

Change in maximum density, corrected for the printing difference

Five independent steps agreeing to ±0.02 about a mean of 0.20 is a result at more than six times the threshold. One step reading 0.20 would not have been.

Upper-scale slope. Take two steps on the slope four apart, so 0.60 in nominal log exposure. On C they read 0.72 and 1.70, a slope of (1.70 − 0.72) ÷ 0.60 = 1.63; on T, 0.78 and 1.86, a slope of 1.80. The change is +0.17, about a 10 per cent increase in upper-scale gradient — which is what “increases upper-scale contrast” means once it is a number.

Where it starts. The difference first exceeds 0.03 at the step whose control density is 0.36. Below that, this session detected nothing; above it, the effect grows monotonically. Note the form of that sentence: it is a statement about your threshold as much as about the toner.

Third, compare the three papers — and compare only the differences. Three ΔDmax figures, three slope changes, three thresholds. Do not compare absolute densities: the papers were given different exposures, have different base tints, and the reflection scale is relative. The blocked design bought you the right to compare changes, which is what the makers’ claims are about anyway. The expected ranking is warm > neutral > cool; if yours differs, ask whether the departure exceeds all three thresholds, because a ranking made of differences smaller than the noise is not a ranking.

Fourth, be careful with colour. What you may write is a ranked, referenced statement in the conservation vocabulary: which paper moved most, in which direction, against its own control under a named light. What you may not write is a magnitude, an invented colour name, or a comparison with anyone else’s print.

!What this session does not establish, at any confidence

Nothing about permanence. Four minutes in a tray is not an ageing test. Kodak’s claim that toning converts the image to an inert compound, and that all their toners protect the image whether or not they shift its colour, is a claim about decades. What this page measures is a change in density and hue on the day. Whether that corresponds to protection, and how anyone would know, is the archival-evidence page.

Nothing about a fourth paper. Kodak’s own list of what governs the effect includes the emulsion, the surface, the stock tint, the dilution, the time and the processing — and you held four of those constant by choosing them, not by discovering they do not matter.

Nothing about another dilution, another time, or another bottle. HARMAN name sodium selenite, Moersch names sodium selenate, Kodak name neither, and a number measured with one is not transferable to another. This is why the lot number is in the log.

Nothing about fibre-base paper. Every number here is from a resin-coated print with a four-minute wash. ILFORD’s fibre sequences put the toner inside a washing-aid bath and finish with a thirty-minute wash, which is a different treatment rather than a longer one.

Fifth, name the two measurements you would most want to repeat: every figure above rests on one sheet per paper.

Troubleshooting

What you see	Where it came from	What to do
Pass 1 residuals show a steady offset between T and C	The two exposures were not equal — lamp drift, or the head or aperture moved	Correct pass 2 step by step with the pass 1 residual and say so. Next time warm the lamp and expose back to back
A difference at base white above the noise floor	A stain, not a toning effect. Kodak: an exhausted fixing bath leaves insoluble silver compounds that form a dark yellow stain on meeting a toner	The fault is the printing session’s fixer. Fresh two-bath fixer, and check the running total
General yellowing of a whole piece	Prolonged fixing let solution into the base, which Kodak state makes selenium- and sulfide-toned prints turn yellow	Fix to the sheet’s time and no longer. That piece is not recoverable
Round purple spots	Air bubbles trapped between or under prints during fixing, which Kodak name for selenium and sulfide toning specifically	Purple spots from fixer air bubbles: separate the prints, keep them moving
A darker band along the cut edge	Toner entering the paper core through the fresh cut — Kodak’s warning about resin-coated edges	Toner edge penetration on RC. Discard the outermost patches; keep the wet time under fifteen minutes
Uneven change across one piece	The pieces overlapped in the dish, or agitation stopped	Uneven toning: a bigger dish, and rock continuously
Almost no measurable change on any paper	An aged or exhausted bath — HARMAN state the rate slows progressively as a solution is used and ages — or a bath below temperature	Check the bottle’s date and the bath’s temperature before concluding anything about paper
The warm paper changed less than the cool one	Either a genuine result, or exposures that put the two papers on different parts of their curves	Check that step 1 was on the maximum-black plateau for both: a paper whose deepest step never reached Dmax cannot show a Dmax change

Clean-up

Bottle the working toner while still gloved, through its own funnel, into the labelled opaque bottle: product, dilution, dates, what it has toned. Fill it as full as you can, because HARMAN’s six-month figure is for a full bottle.

Everything the toner touched is rinsed into the collected stream — dish, tongs, graduate, funnel, thermometer — three times with a small volume rather than once with a large one. Wash gloved hands, remove gloves inside out, wash hands. Wipe the bench, and leave the ventilation running fifteen minutes with the room empty.

Storage

The concentrate. HARMAN give unopened bottles two years at 5 to 20 °C and six months once opened. Store it upright, cool, dark, in secondary containment, away from anything acid.

The working solution. Six months in a full capped bottle, one month half-full, seven days in an open tray. An aged bath works slower, so if you re-run from a bottle its history is part of the method.

The prints. All six pieces in one labelled envelope. They are the only record that can be re-measured, and re-measuring them in six months against a re-calibrated instrument tests your uncertainty statement better than anything on this page. The step wedge goes back flat, dark and handled by the edges.

Disposal considerations

The chemistry first, because the rule follows from it. The bath holds a soluble selenium salt classified very toxic to aquatic life with long-lasting effects — Aquatic Acute 1 and Aquatic Chronic 1 for the selenite on HARMAN’s composition table, the same pair for the selenate on Moersch’s — with thiosulfate, sulfite and whatever silver the bath’s solvent action removed. Dilution does not remove an aquatic hazard; it relocates it.

What the makers say. HARMAN: do not empty into drains, dispose of the material and its container at a hazardous or special waste collection point. Kodak’s guidance for amateurs, generous about almost everything else, puts selenium toners first on the list of what a domestic photographer must not send to the sewer, and gives used Rapid Selenium Toner as the only product in its table with no route open but household hazardous waste collection. Moersch directs his to hazardous waste and forbids the drain.

What the course does. The toner and the stop-bath water that carried it are collected without argument. The wash water is collected too, under the disposal ruling, which reads separately collected home photochemistry as an absolute hazardous entry in the List of Waste — and WM3 is explicit that an absolute entry applies even where the waste displays no hazardous property. Kodak’s amateur guidance would permit wash waters to the sewer; where a manufacturer and the course’s reading of the waste regulations disagree, this part follows the stricter.

The route for a household in England and Wales is the local authority’s household waste and recycling centre or its collection service. Take it in the labelled container it was collected in, and say what it is.

Check your local regulations. They govern, they differ between authorities inside one country, and they change. What does not change is the composition of the liquid in the bottle.

Questions

1. Your pass 1 residuals show T reading 0.04 higher than C at every step from toe to maximum black. What has happened, is the session salvageable, and what do you do to the pass 2 numbers?
2. The neutral paper gives ΔDmax = 0.02 and your replaced-sample repeatability is 0.015. Write the sentence you are entitled to put in the conclusion, and the sentence you are not.
3. Why does this page set the toning endpoint with a clock when every printing page tells you to judge by eye, and what would go wrong if you set it by eye here?
4. Kodak’s published curve is POLYMAX Fine-Art Paper at 1:40 for four minutes; yours is a current ILFORD paper at 1+20 for four minutes. Name three things that differ, and say which prevents a comparison of magnitudes and which merely makes it awkward.
5. Eleven of your twenty-one steps came out at maximum black. Is that a fault in the exposure, and what would change if you exposed a stop less?
6. Name two things the sham bath controls for, and one thing it does not.

Further experiments

The second dilution, which is the natural sequel. Repeat at 1+40, Kodak’s other published figure for the same stated purpose, holding four minutes and everything else constant. It would settle whether dilution at fixed time behaves as the chemistry page claims — as a rate control rather than an endpoint control. Half the ΔDmax at 1+40 means the reaction was still climbing at four minutes and the dilution is setting a rate; nearly the same ΔDmax means it had essentially finished in both.

The time series, done properly. This page gets its time information from four lifts of one piece, a trajectory of appearance rather than a series of measurements. Print four T scales and one C scale per paper, tone them 1, 2, 4 and 8 minutes in the same bath, and you have ΔDmax against time with the control shared. It costs two more sheets per paper and is the only way to see whether four minutes was the plateau.

Moersch’s bleach diagnostic, on a sacrificial piece. Tone a spare T piece and bleach it in a ferricyanide-bromide bleach: untoned silver converts, selenide does not, so what survives maps how far the toning reached. It is done on a spare because a print carrying bleached, untoned silver bromide is no longer archival and must be fixed out or toned again.

The fibre-base version, run as ILFORD’s optimum permanence sequence with selenium: fix one minute, tone in toner diluted with working-strength washing aid instead of water, ten minutes of washing aid, thirty minutes of final wash. Note before you start that ILFORD state short washes give MULTIGRADE FB WARMTONE a cooler image colour than long ones — on that paper the wash is part of the colour result, a confounder the resin-coated route does not have.

Recap

• The control is the other half of the same print, cut from one sheet that carried the same wedge twice, and it is treated rather than neglected: plain water at the same temperature for the same four minutes, because a wetting cycle changes density and an untreated control would put that change into the result.
• Paper is a block, not a variable. Three within-sheet comparisons, none of which crosses papers — which is what makes a relative reflection scale sufficient.
• One dilution and one time, both chosen because two makers publish them: 1+20 for four minutes at 20 °C, inside Kodak’s 2-to-8-minute window and at the top of HARMAN’s 2-to-4. The wet-time budget of 14.3 of ILFORD’s 15 minutes fixes the toning time as much as any chemistry does.
• The clock sets the endpoint here, against the practice of every printing page in the course, because an independent variable set by eye is not independent.
• Read every step twice. The first pass is not a baseline but the proof that the halves were ever the same print, and it supplies the noise floor that decides what counts.
• Three numbers come out — the change in maximum density, the change in upper-scale slope, and the density at which the difference first clears twice your repeatability — each quoted with the figure that limits it. Hue is described, not measured, in the vocabulary Getty and the AIC use, against the paper’s own control under one named light.
• The session says nothing about permanence, a fourth paper, another dilution or another maker’s bottle. It says what one treatment did to three papers on one day, which is more than any source in this corpus will tell you.

Check your understanding

Question 1. Why must the untoned control be cut from the same sheet as the toned piece rather than printed as a separate sheet at the same exposure?

• To save paper, since three sheets is cheaper than six
• Because paper batch, exposure and development all shift maximum density, so a separate sheet would confound those shifts with the toning effect
• Because a separate sheet could not be measured on the same densitometer
• Because the manufacturers require a within-sheet control

Show the answer and why

Answer: Because paper batch, exposure and development all shift maximum density, so a separate sheet would confound those shifts with the toning effect

The quantity being measured is a density difference of the order of 0.1 to 0.2, and every one of the things that differ between two separately printed sheets — a fractional change in exposure, a dish that had cooled, a different part of the box — moves maximum density by an amount of the same order. Cutting one sheet in half removes all of them at once, and the pass 1 reading then proves it worked. Saving paper is a side effect, and no maker asks for this design; it is the experiment protecting itself against its own noise.

Question 2. This page sets the toning endpoint with a timer, while HARMAN’s own sheet and every printing page in the course tell you to judge against a reference print. Why the difference?

• Because HARMAN’s method only works with their own toner
• Because the eye cannot see a change of 0.2 in density
• Because the treatment is the independent variable here, and a variable set by appearance is decided by the least repeatable instrument in the room and would make the three papers incomparable
• Because timing is more accurate than looking in every circumstance

Show the answer and why

Answer: Because the treatment is the independent variable here, and a variable set by appearance is decided by the least repeatable instrument in the room and would make the three papers incomparable

In a printing session the endpoint is an appearance, so the eye is the correct instrument and HARMAN’s three-dish reference method is the right procedure. In an experiment the treatment must be identical across the blocks, and "until it looks right" is not identical across three papers that look different to begin with. The lifts still happen and are still visual — they record the trajectory — but the eye is demoted from controller to observer. Option two is wrong in the other direction: the eye is a fine comparator between two pieces side by side, which is exactly the job the hue reading gives it.

Question 3. Your difference curve is flat at about 0.20 across five adjacent steps at the shadow end, then falls smoothly to zero towards base white. What does the flat region tell you?

• The densitometer saturated and the readings there are worthless
• Those steps were all already at maximum black, so they share one density that the toning raised together — five agreeing readings of one quantity rather than five separate results
• The toner exhausted itself in the shadows and stopped working
• The wedge steps are not evenly spaced at that end

Show the answer and why

Answer: Those steps were all already at maximum black, so they share one density that the toning raised together — five agreeing readings of one quantity rather than five separate results

A step wedge spanning 3.00 in log exposure is about three times longer than a paper’s exposure scale, so several steps at the low-density end of the wedge all receive more than enough exposure and land on the same maximum-black plateau. They are therefore five measurements of one number, not five numbers, and their agreement to within your repeatability is what turns a single reading into a result. Saturation would show as a ceiling in the instrument rather than a plateau that moves by 0.20 when the print is toned.

Question 4. A reader reports "selenium toning raised Dmax by 0.20 and therefore protects the print." Which of the two claims does this session support?

• Both, since a higher Dmax means more silver has been converted
• Only the density claim; conversion is partial and unmeasured here, and a four-minute session is not an ageing test
• Neither, because a relative reflection scale cannot support a density claim
• Only the protection claim, since Kodak state that all their toners protect the image

Show the answer and why

Answer: Only the density claim; conversion is partial and unmeasured here, and a four-minute session is not an ageing test

The density figure is exactly what the design measures, and a relative scale is sufficient for it because the quantity is a difference between two halves read on one instrument in one session. The protection claim is of a different kind: it is about behaviour over decades, it depends on how much of the silver was converted rather than on how much the density moved, and Moersch’s own bleach test found unconverted silver after a longer, stronger treatment than this one. Kodak’s sentence is a manufacturer’s claim about their products, and the archival-evidence page is where it is examined rather than repeated.

Question 5. Why does this page require all six pieces to be air-dried at room temperature rather than in a warm-air dryer?

• Because heat would damage resin-coated paper
• Because Kodak record that drying with heat causes a shift to a cooler tone with some paper and toner combinations, which would enter the measurement as a treatment effect
• Because a warm-air dryer would not fit six pieces
• Because the emulsion must dry slowly for the selenide to form

Show the answer and why

Answer: Because Kodak record that drying with heat causes a shift to a cooler tone with some paper and toner combinations, which would enter the measurement as a treatment effect

Kodak state it directly and recommend setting a dryer to its lowest settings, adding that the amount of toning may have to be adjusted to compensate. On this page the danger is subtler than a spoiled print: if the toned pieces met heat and the controls did not, a drying artefact would be indistinguishable from a toning result. The fix is not to avoid heat as such but to make the drying identical for all six, and room-temperature air is the easiest identical thing to arrange. The selenide has finished forming long before the print is dry.

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