Staining and Tanning Developers

Bergger’s instructions for PMK change four things that have nothing to do with development. The stop bath must not be acid. The fixer must be non-tanning. The wash runs 20 to 30 minutes rather than the usual five to ten, because “the image colouring intensifies during washing”. And a hypo eliminator — a product whose entire purpose is to shorten a wash — must not be used, because it “would weaken the colouring of the negative”.

A developer that reaches three baths downstream of itself is telling you that it left something behind in the film. It did: a pyro negative carries two densities in the same layer, one made of silver and one made of the developer’s own oxidation product, and every instruction above exists to protect the second one.

What the course can say about the product, and what it cannot

This page begins with its gap rather than ending with it, because everything else is built on top of the gap and a reader should know that from the start.

Established, from sources this course has read. The oxidation product of pyrogallol is coloured. It is deposited in the film alongside the silver, in proportion to the amount of development. It hardens the gelatin where development happened. Sulfite suppresses it, in a dose-dependent way.

Not established, and not asserted anywhere on this page. What the coloured product is. What its formula is. What reaction forms it. And by what mechanism it cross-links gelatin. The pyrogallol encyclopaedia entry says the same in the same words, and this lesson does not quietly supply what that page says the course could not find.

⚗What a reaction scheme would need, and why there isn't one here

Every other agent in this part gets an oxidation equation. Metol gets one, hydroquinone gets two competing ones, ascorbate gets one. Pyrogallol gets none, and the reason is worth understanding, because it is a model of what Rule 1 costs.

To write the first oxidation step you would have to know three things: which of pyrogallol’s three hydroxyls are oxidised and to what, whether that first product is the species that colours the film, and whether it is also the species that reacts with the gelatin. This course knows none of the three from a document it has read, and no equation for pyrogallol’s oxidation appears on this page. It would be easy to write one that balanced, and that is exactly the trap: a balanced equation looks like knowledge, and it is arithmetic. Balancing is a test an equation must pass, not evidence that it describes anything.

The honest position is that pyrogallol has three hydroxyls where hydroquinone has two, so it has more ways to be oxidised and more ways for the products to react further with each other and with the gelatin, and that the coloured material in a pyro negative is almost certainly a mixture rather than a compound. Kodak’s own 1928 primer, which is happy to give equations elsewhere, describes the pyro product only as “oxidized pyrogallol” and leaves it there. When a manufacturer’s own chemists decline to name something, that is information.

Sulfite is the dial, and a staining developer is that dial turned down

Kodak’s primer teaches the preservative through pyro, because pyro shows it best, and it does so as a graded experiment rather than an assertion: no sulfite gives a very yellow negative whose image consists partly of silver and partly of oxidised pyrogallol; sulfite present gives a much less yellow one, because the sulfite is oxidised instead of the agent; a great deal of sulfite gives almost as blue an image as Elon, whose oxidation product is not deposited in a coloured form.

The lesson on the alternative agents drew that series. What follows from it is the design constraint that shapes every formula on this page:

A staining developer cannot carry a normal preservative, because the preservative’s job is to destroy exactly the substance the stain is made of. There is no formulation that gets both. A pyro developer is therefore a badly preserved developer on purpose, and every practical difficulty with these formulae — the two-part storage, the short working life, the sensitivity to how much air the solution meets — descends from that single fact.

Proportional stain, general stain, and how to tell them apart

The stain a formulator wants is the one that tracks the silver. Bergger describes it precisely: “a yellow-green tint surrounds each silver grain and fills the usually empty space between them and becomes an intrinsic part of the image”, so that “the density of a pyro negative is therefore the conjunction of two densities, that of the silver and that of the coloration”.

Where the stain sits, and what tanning does to the gelatin around it

1. 1Proportional stain — coloured product deposited in proportion to the development, filling the space between the grains
2. 2Tanned gelatin — the same product hardening the layer where development happened; it swells less when wet
3. 3General stain — colour in areas that did not develop; not image, and behaves as base density

A mechanism drawing. The course has no micrograph of a stained negative and describes none; the identity of the coloured product is not known to this course and is not implied by the drawing.

General stain is the same colour in the wrong place: an overall tint that reaches the clear areas of the negative, which never developed and therefore have no image density to be proportional to. It comes from oxidation product formed in the solution rather than at a grain, and from oxidation product that has not been washed out, which is why the wash matters. Diagnostically the two are easy to tell apart on a light box — proportional stain leaves the film base and the rebate clear; general stain colours them too.

Stain as density: which colour you measure it in decides what it is worth

A densitometer gives a different answer for a stained negative depending on what light it uses, and this is not an artefact. A yellow-green deposit absorbs blue strongly and green weakly and red hardly at all, so:

• Read in visual or green light, the stain contributes modestly and the negative looks close to what the silver alone would give.
• Read in blue or ultraviolet light — which is what a printing paper mostly sees — the stain contributes heavily, and the negative behaves as though it had far more contrast than a visual reading suggests.

Why a stained negative has two characteristic curves

• Blue or UV density: silver plus stain
• Visual or green density: silver alone

Show the numbers behind this plot

Two curves are plotted against the same relative log exposure axis, both starting from a base density of about 0.1 at the far left. The lower curve, labelled silver density read in green or visual light, rises through a toe and then climbs at a moderate gradient to about 1.1 at the right-hand end. The upper curve, labelled total density read in blue or ultraviolet light, follows the same toe but climbs more steeply, reaching about 1.75 at the same exposure, so that the vertical gap between the two curves widens continuously from left to right. The widening gap is the stain, and because it grows with exposure it acts as extra contrast rather than as extra base density. A dashed horizontal reference line marks the common base. The caption states that the shapes are drawn to show the argument and were not measured, that no numbers on the plot may be quoted, and that the essential claim is only that the two curves share a base, diverge as exposure rises, and therefore give two different contrast readings from one negative.

Series	Relative log exposure	Density
Blue or UV density: silver plus stain	-2.00	0.10
Blue or UV density: silver plus stain	-1.60	0.12
Blue or UV density: silver plus stain	-1.30	0.20
Blue or UV density: silver plus stain	-1.00	0.38
Blue or UV density: silver plus stain	-0.60	0.72
Blue or UV density: silver plus stain	-0.20	1.08
Blue or UV density: silver plus stain	0.20	1.38
Blue or UV density: silver plus stain	0.60	1.60
Blue or UV density: silver plus stain	1.20	1.76
Visual or green density: silver alone	-2.00	0.10
Visual or green density: silver alone	-1.60	0.11
Visual or green density: silver alone	-1.30	0.17
Visual or green density: silver alone	-1.00	0.30
Visual or green density: silver alone	-0.60	0.52
Visual or green density: silver alone	-0.20	0.72
Visual or green density: silver alone	0.20	0.90
Visual or green density: silver alone	0.60	1.02
Visual or green density: silver alone	1.20	1.10

Shapes drawn to show the argument, not measured from a negative; no number here may be quoted. The claim is the divergence: one negative, two densities, and therefore two different contrast readings depending on the light used to read it. 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.

On variable-contrast paper: an inference, labelled as one

ILFORD’s technical information on MULTIGRADE papers explains how they work, and the mechanism is entirely about the blue-to-green ratio of the printing light. Exposure to blue light activates all the emulsions and gives a high-contrast image; exposure to green light activates only part of them and gives a low-contrast one. Hence the filters: “a magenta filter absorbs green light and transmits blue” for hard, “a yellow filter absorbs blue and transmits green” for soft.

Now put a yellow-green negative in front of that paper. The stain is itself a yellow filter, and it is densest in the highlights.

!This is the course's inference, not a manufacturer's statement

Two sourced facts stand behind the paragraph above: Bergger states that the PMK stain is yellow-green and lies in proportion to the image, and ILFORD states that a yellow filter lowers the contrast of a variable-contrast paper. Joining them is the course’s reasoning, and no document it has read states the conclusion.

What the inference predicts is that a stained negative printed on variable-contrast paper behaves as though a soft filter had been applied selectively to the highlights, which is the highlight compression that pyro’s advocates describe — and that the same negative on a graded paper, whose contrast is fixed and whose sensitivity is mostly blue, behaves quite differently, with the stain adding straightforward printing density rather than local softness.

Treat that as a hypothesis you can test in an evening once you have both papers, not as a result. It is also a good example of the difference between a mechanism that must be true and a mechanism that merely fits: the blue-absorbing property of a yellow stain is not in doubt; how much of it there is in your negative, at your densities, is entirely unmeasured here.

For alternative processes, which print by ultraviolet, the same logic points the other way and the evidence is weaker still. Bostick and Sullivan’s Pyrocat-HD sheet reports that “other users have reported reduced printing times with UV light sources compared with PMK negatives (for alt process work) due to the different stain color”. That is a manufacturer relaying user reports — a tier-3 claim inside a tier-1 document — and the course records it as such rather than as evidence that one stain colour prints faster than another.

Tanning, and the four things it changes

Eder’s history dates the discovery to the end of the 1870s: Leon Warnerke found the tanning action of pyrogallol on silver bromide plates and reported in 1881 that only the unexposed parts of such a film remained soluble in warm water, the exposed and tanned parts being insoluble. Eder had already pointed out that the relief left by alkaline pyrogallol without sulfite could be made high enough to mould from and used as a printing plate. For two generations, the tanning was the reason to use pyro at all.

For a photographer today it changes four things.

1. The layer swells less where it developed. A hardened region takes up less water, which changes how everything after the developer penetrates it.
2. The fixer must not harden as well. Bergger is unambiguous: “a non-tanning bath is essential for good subsequent coloration of the negative”, and recommends an acid-free fixer. A hardening fixer on top of a tanned layer locks the stain’s precursors in or drives them out, depending on whom you ask; what is documented is only that the maker forbids it.
3. The wash lengthens rather than shortens. Twenty to thirty minutes, because the colouring intensifies during it — which means washing is part of image formation here and not merely the removal of residues.
4. Edge behaviour. Bostick and Sullivan call Pyrocat-HD “a semi-compensating, high-definition developer”, and Bergger says PMK gives “negatives with very sharp outlines and very detailed highlights”. Both are manufacturers describing their own product; neither offers a mechanism, and the course does not supply one. What it can say is that these are low-sulfite, high-dilution, single-agent baths, which is the recipe for adjacency effects whether or not the tanning contributes anything of its own.

One claim you will meet and will not find here. Pyro is often said to make a negative more permanent, on the argument that the stain shields the silver from oxidation. No document in this course’s corpus makes that claim or supplies evidence for it — not Bergger’s datasheet, not Bostick and Sullivan’s, not Kodak’s primer, and not the conservation literature the course reads for permanence questions. The tanning is documented, the stain is documented, and the leap from either to image permanence is not. Treat it as an open question, and notice that it would be testable: two identically exposed negatives, one stained and one not, accelerated and read against each other.

The four formulae, and what provenance each of them has

Rule 6 gives four different answers to the same question here, and the differences are the lesson.

Formula	What the course holds	What it prints
Kodak D-1, standard A.B.C. pyro	Kodak’s own 1928 primer, with all three stock solutions and both working dilutions	The whole formula
PMK	Bergger’s 2020 datasheet: dilution, capacity, temperature, processing, hazards — and no ingredient list	Behaviour, dilution and handling only
Pyrocat-HD	Bostick and Sullivan’s kit sheet: behaviour, agitation schemes, comparative claims — and no named agents at all	Behaviour only
510-Pyro	A development-time chart whose data is credited to a community database, with no composition	Nothing at all

Kodak D-1 is published and is printed. Stock A carries 60 g of pyrogallol per litre with 9.8 g of sodium bisulfite and 1.1 g of potassium bromide; stock B carries 105 g of sodium sulfite per litre; stock C carries 75 g of sodium carbonate per litre. For tray work, one part of each with seven of water, which makes a working solution of 6 g of pyro, 10.5 g of sulfite and 7.5 g of carbonate per litre, 7 to 9 minutes at 18 °C. The tank version uses eleven parts of water instead of seven and runs 13 to 15 minutes.

Read the working numbers against D-76 and the whole design is visible at once: 10.5 grams of sulfite per litre against D-76’s hundred, a tenth as much. That is not a small preservative; it is a deliberately inadequate one, and it is the difference between a developer that hides its oxidation product and one that prints it.

PMK is a manufacturer’s product with an unusually informative datasheet and no formula on it. Bergger states that it is “a pyrogallol-based developer… adapted to modern films by Gordon Hutchings in the 1980s”, supplied as solution A of 250 mL and solution B of 500 mL, used at 1+2+100 to make 25 litres of working solution, with a capacity of 1,000 cm² of film per litre, an hour of working life in an open vessel, and a stated shelf life of up to ten years for both concentrates even half-filled. None of that is a composition, and this course prints none.

Pyrocat-HD goes further in the same direction: the kit sheet describes what the developer does at length and does not name a single ingredient, so it is evidence about behaviour and claims and about nothing else. King’s cited advantages over PMK — about a third of a stop more effective speed, 10 to 15 per cent shorter times, more consistent staining, lower toxicity, no streaking or mottling with reduced agitation — are claims by the formulator, reported by his supplier, and the course labels them that way.

510-Pyro is where the discipline is most visible. The document in the corpus is a development-time chart. It carries no ingredients, no quantities and no mixing instruction, and its header credits the times to a community database rather than to the supplier’s own measurement. There is therefore nothing to print, and the question of triethanolamine as a solvent — which the curriculum asked the course to verify, along with its hazards — does not arise, because the course cannot establish that it is in the product. A formula the course cannot source is not a formula the course discusses the safety of.

🕰Historical pyro, and the one form that is not taught as procedure

Wall’s 1924 formulary carries several pyro-soda developers in two solutions, from Wratten and Wainwright, Bothamley, Claudy, Harris and Munkman, along with a pyrocatechin developer at 10 g of catechol and 40 g of sulfite in 500 mL of solution A against 100 g of sodium carbonate crystals in 500 mL of B, for an hour at 18 °C. These are published, and they are the record of what was actually done.

Pyro-ammonia is the exception the course marks and does not give as a procedure. It was the original gelatin-plate developer, and Eder records what was wrong with it: delicate results, but a yellowish or brownish stain that “often spoiled the whole gelatin layer”, and solutions that were difficult to keep. Wall’s verdict by 1924 is that it “was once the favorite developer, but is rarely used now on account of its variability, due to the evaporation of the ammonia”. The course’s own restriction on ammoniacal silver, set out in Part II, is a separate and stronger reason. It is taught as history.

Two-part storage, and the logic that produces it

A staining developer has to solve a problem it created. It cannot carry enough preservative to keep, because the preservative is what kills the stain. So it keeps the agent and the alkali apart until the moment of use, and preserves the agent bottle with an acid sulfite instead of a neutral one.

Kodak Limited’s 1949 handbook states the general rule for the whole class: developers “which are particularly susceptible to aerial oxidation often are divided into two or three solutions in which the developing agent is kept separate from the alkali, thus reducing oxidation”. The 1928 primer gives the chemistry underneath: a developing agent stored for a long time keeps best with an acid sulfite such as sodium bisulfite rather than sodium sulfite, which is slightly alkaline, and bisulfite “keeps satisfactorily in more dilute solutions and is a better preservative than sulfite in the absence of carbonate”. It names pyro among the readily oxidisable agents customarily kept that way.

Kodak’s own D-1 does exactly this: pyro with bisulfite and bromide in A, the sulfite alone in B, the carbonate alone in C, and the keeping-properties table lists D-1 as stored in three solutions. PMK and Pyrocat-HD are the same idea in modern packaging — an A and a B that meet in the tank.

The corollary matters more than the rule. The stability of a two-part developer belongs to the parts, not to the mixture. Bergger’s ten-year claim is for the concentrates; the working solution is given one hour in an open vessel. Nothing about a long-lived concentrate implies a long-lived bath, and treating the two as the same number is the commonest way to spoil a session with these developers.

Toxicology: two agents, two different levels, and no procedure on this page

The pyrogallol and catechol entries carry the hazard data and the reasoning behind each classification; this section states the outcome and what follows for practice.

Pyrogallol is Level B — the advanced home laboratory. Its aggregated GHS classification is Warning with the irritant and health-hazard pictograms, and three statements are unanimous across every reporting notifier: harmful in contact with skin, harmful if inhaled, and suspected of causing genetic defects. There is no NIOSH Pocket Guide entry and no EH40 workplace exposure limit, and HSE’s own introduction to that list warns that absence from it does not indicate that a substance is safe. Bergger’s own datasheet is blunter than any of that: pyrogallol is “toxic to health, causing kidney, liver, circulatory disorders, or even death”, is toxic by inhalation, skin contact and ingestion, is a phenol and can cause burns, and brief skin contact leaves a dark stain while prolonged contact can cause a burn resembling a heat burn.

Catechol is Level C — engineered extraction, controlled waste and supervision, which a home does not have. Its classification is Danger, with an acute-toxicity pictogram that pyrogallol does not carry, a minority but substantial notification of “may cause cancer”, and a NIOSH skin notation meaning that absorption through intact skin contributes materially to exposure. The course’s position is that a reader may study catechol chemistry and may not weigh catechol powder at home.

⚠Safety

This lesson gives no procedure, and that is a deliberate outcome rather than an omission. Neither agent is weighed, dissolved or used anywhere on this page.

The controls that a Level B assessment of pyrogallol would require are on the encyclopaedia page and are not repeated here: extraction or an enclosure for weighing the solid, nitrile gloves, eye protection, an apron, no open film or paper in the room, and tongs rather than fingers. The single most useful piece of advice the course has found on the subject is Florida Atlantic University’s, which does not tell darkroom workers how to weigh pyrogallol but tells them to avoid pyrogallol and catechol and to substitute phenidone. A reader who wants a stained negative and has no extraction should buy the liquid concentrate rather than the jar of solid, which removes the weighing step entirely and is why the products discussed above are sold as liquids.

⁇A manufacturer's sheet that disagrees with its own table

Bergger’s PMK datasheet states that because the stain is an intrinsic part of the image, “the sensitivity of the film and its printing qualities are increased”. Two pages later, the sheet’s own time and temperature chart lists the meter setting for each film: FP4 Plus at 80 against a box speed of 125, HP5 Plus at 200 against 400, Delta 100 at 64, Pan F Plus at 32 against 50 and Tri-X 400 at 250.

Every one of those is between half and two-thirds of a stop below the film’s rated speed. The sheet therefore claims increased sensitivity in its prose and tabulates a speed loss in its data, and the course does not have the information to reconcile them. Two readings are available and it declines to choose: the prose may mean printing speed, since a negative with more blue density prints more slowly and therefore appears to hold more, or the claim may simply be marketing that the technical table does not support.

Bostick and Sullivan’s sheet gives the same tension a different shape, quoting King’s claim of “one third of a stop greater effective film speed” for Pyrocat-HD relative to PMK — a comparison that only makes sense if PMK itself loses speed. Where a manufacturer’s prose and its own table disagree, this course follows the table and says which it followed.

Recap

• A pyro negative is two densities in one layer: silver, and a coloured oxidation product deposited in proportion to development. Everything unusual about processing one exists to protect the second.
• The course cannot name the coloured product, give an equation for it, or describe the cross-linking mechanism, and does not. Three sourced facts — it is coloured, it deposits with the silver, it hardens the gelatin — are what the whole page is built on.
• Sulfite is the dial. Kodak’s graded experiment runs from a very yellow negative at zero sulfite to an almost blue one at high sulfite. A staining developer is a deliberately under-preserved developer, and every practical difficulty follows from that.
• Proportional stain is image; general stain is fog with a colour. The rebate tells you which you have.
• The stain reads differently in blue and in green light, which is why a stained negative has two contrast values. Its behaviour on variable-contrast paper is the course’s inference from two Tier-1 statements, not a claim either source makes.
• Four formulae, four provenance verdicts. Kodak D-1 is printed in full; PMK and Pyrocat-HD are taught as behaviour because their sheets carry no composition; 510-Pyro is taught as nothing, because the only document held is a time chart with community-sourced data.
• Two-part storage is forced by the chemistry, and the concentrates’ shelf life says nothing about the working solution’s — ten years against one hour, on the same sheet.
• Pyrogallol is Level B and catechol is Level C, and this lesson gives no procedure for either.

Check your understanding

Question 1. Why can a staining developer not simply be given more sulfite to improve its keeping?

• Because sulfite raises the pH too far
• Because the sulfite intercepts the oxidised developing agent, which is the substance the stain is made of, so preserving the bath destroys the image it is meant to make
• Because sulfite precipitates pyrogallol out of solution
• Because sulfite would harden the gelatin prematurely

Show the answer and why

Answer: Because the sulfite intercepts the oxidised developing agent, which is the substance the stain is made of, so preserving the bath destroys the image it is meant to make

Kodak’s graded experiment is the direct evidence: no sulfite gives a very yellow negative, sulfite gives a much less yellow one because the sulfite is oxidised instead of the agent, and a great deal of sulfite gives almost as blue an image as a metol developer. The preservative and the stain are competing for the same species, so the trade is absolute. Kodak D-1 carries 10.5 g of sulfite per litre in the working solution against D-76’s 100, which is the design decision written as a number.

Question 2. A pyro-developed negative is read on a densitometer in visual light and again in blue light. What do you expect, and why?

• The two readings will agree, because density is density
• The blue reading will be higher, and the gap will widen with exposure, because the yellow-green stain absorbs blue strongly and lies in proportion to the image
• The visual reading will be higher, because the eye is more sensitive than a blue filter
• The blue reading will be higher by a constant amount at every step

Show the answer and why

Answer: The blue reading will be higher, and the gap will widen with exposure, because the yellow-green stain absorbs blue strongly and lies in proportion to the image

A yellow-green deposit absorbs blue light far more strongly than green, so it contributes much more to a blue reading than to a visual one. Because the stain is proportional to development rather than uniform, the difference grows with exposure — it is extra contrast, not extra base density. That is why one stained negative has two contrast values and why the light your printing paper sees decides which of them matters.

Question 3. The Bostick and Sullivan sheet for Pyrocat-HD names no developing agent anywhere. What may this course legitimately take from it?

• The agitation schemes and development times it publishes
• The comparative claims it attributes to Sandy King, labelled as the formulator’s claims
• A composition for Pyrocat-HD, inferred from the fact that it is described as a pyro developer
• The warning that dichroic fog may result from extended development of high-speed films

Show the answer and why

Answer: The agitation schemes and development times it publishes, The comparative claims it attributes to Sandy King, labelled as the formulator’s claims, The warning that dichroic fog may result from extended development of high-speed films

A manufacturer sheet is Tier 1 evidence for what it actually states: procedures, times, warnings, and claims correctly attributed to whoever made them. It is not evidence for what it does not state. Inferring a composition from a product category is exactly the move Rule 6 forbids, and the fact that the inference would probably be roughly right is not relevant — a course that publishes probably-right formulas has no way to tell you which ones those are.

Question 4. Bergger states a shelf life of up to ten years for the PMK concentrates and one hour for the working solution in an open vessel. What accounts for the difference?

• The concentrates contain a preservative that is diluted away
• The concentrates keep the agent away from the alkali and hold it in an acid solution, and dilution then exposes a small quantity of agent to a large volume of alkaline, aerated water
• The working solution is used at a higher temperature
• The ten-year figure refers to the unopened bottles only

Show the answer and why

Answer: The concentrates keep the agent away from the alkali and hold it in an acid solution, and dilution then exposes a small quantity of agent to a large volume of alkaline, aerated water

Two-part storage is the whole mechanism, and Kodak stated the rule for the class in 1949: readily oxidised developers are divided so the agent is kept away from the alkali. Alkali is what makes an agent active and therefore also what makes it oxidise. Dilution then compounds it — a hundredfold dilution means a very small amount of agent facing the oxygen dissolved in a large volume of water, which is the same arithmetic that made Wratten and Wainwright’s dilute rodinal take longer in aerated water.

Question 5. Pyrogallol sits at Level B in this course and catechol at Level C, although both are staining developing agents of the same chemical family. What separates them?

• Catechol is a stronger developer and therefore more dangerous
• Catechol carries an acute-toxicity classification, a substantial minority carcinogenicity notification and a NIOSH skin notation, so the recognised control is engineered extraction rather than gloves and ventilation
• Pyrogallol has an exposure limit and catechol does not
• Catechol has no manufacturer selling it for photographic use

Show the answer and why

Answer: Catechol carries an acute-toxicity classification, a substantial minority carcinogenicity notification and a NIOSH skin notation, so the recognised control is engineered extraction rather than gloves and ventilation

A level is assigned to a procedure against the hazard of the substances in it, and the deciding question is what control the classification calls for. Pyrogallol’s record is serious but its controls are gloves, eye protection and extraction for the powder, which a well-equipped home laboratory can provide; catechol’s acute toxicity, skin notation and carcinogenicity notification put the recognised control at a fume cupboard with managed waste, which a home does not have. Neither substance is weighed anywhere on this lesson page.

Question 6. Bergger’s prose claims that PMK increases film sensitivity, while its own time-and-temperature chart lists FP4 Plus at EI 80 and HP5 Plus at EI 200. How does this course handle the contradiction?

• It follows the prose, because the manufacturer knows its own product
• It ignores both, because manufacturer literature is unreliable
• It reports both, follows the table, and says which it followed, offering the possible reconciliation without asserting it
• It averages the two

Show the answer and why

Answer: It reports both, follows the table, and says which it followed, offering the possible reconciliation without asserting it

Rule 7 asks that fact and interpretation be distinguished, and this is a case where a single Tier-1 document contains a claim and data that pull against each other. Data beats prose within one document, but the disagreement is itself information a reader should have — the prose may mean printing speed rather than exposure speed, since a negative with more blue density prints more slowly. Naming both readings and saying which was used is more useful than quietly discarding one.

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