Kodak IN-5

Kodak Limited printed five intensifiers in 1949. One is mercury, one is uranium, and two are built on chromium(VI); those four are historical study in this course and carry no procedure. This is the fifth. It is made of silver nitrate, sulfite, hypo and Elon — four substances the course already handles elsewhere — and it is the only intensifier in that handbook every reagent of which has a written encyclopaedia entry at Level A or B.

Stock Solution No. 1 — the silver

Ingredient	Quantity	Form the source specifies
Silver nitrate	60 g	crystals
Water	to make 1000 mL	A 6 per cent w/v solution, and the only solution in this formula for which the handbook specifies distilled water. Silver nitrate meets any chloride in tap water as an insoluble halide, so the specification is doing work.
Kodak Limited's own parenthesis is "Store in a brown bottle". Silver nitrate solution darkens in light faster than the solid does.

Stock Solution No. 2 — the precipitant

Ingredient	Quantity	Form the source specifies
Sodium sulfite (anhydrous)	120 g or 60 g (anhydrous)	crystalline
Water	to make 1000 mL	12 per cent w/v as the crystals, 6 per cent as the anhydrous salt. Kodak Limited prints both, as it prints every sulfite and carbonate twice.

Stock Solution No. 3 — the solvent

Ingredient	Quantity	Form the source specifies
Sodium thiosulfate pentahydrate	105 g	hypo
Water	to make 1000 mL	A 10.5 per cent w/v hypo solution - a quarter the strength of the plain hypo fixing bath, and it is here as a ligand rather than as a fixer.

Stock Solution No. 4 — the developer

Ingredient	Quantity	Form the source specifies
Sodium sulfite (anhydrous)	30 g or 15 g (anhydrous)	crystalline
Metol	24 g	'Elon', Kodak's own brand of the same substance
Water	to make 3000 mL	Three litres, not one - the only stock in this formulary made to a volume other than a litre, and it is made large because three of the six parts of the working bath come from it. That works out at 10 g/L of crystalline sulfite and 8 g/L of Elon.
The handbook's general instruction for making up any formula containing Elon is to dissolve the Elon first, because it is readily soluble in warm water but only slightly soluble in sulfite solutions without alkali. That instruction is printed at the front of the handbook rather than under IN-5, and it is the reason for the order given here.

Mixed in this order — the working intensifier, mixed immediately before use

1. Start with 1 part Stock Solution No. 1 — the solution that receives, and it receives in this order or not at all
2. Then add 1 part Stock Solution No. 2 — added slowly, with stirring; a white precipitate appears and is expected
3. Then add 1 part Stock Solution No. 3 — dissolves the precipitate; the solution is left to stand a few minutes until clear
4. Then add 3 parts Stock Solution No. 4 — added last, while stirring, and the bath is used at once

Slowly add 1 part of Solution No. 2 to 1 part of Solution No. 1, stirring to obtain thorough mixing. The white precipitate which appears is then dissolved by the addition of 1 part of Solution No. 3. Allow the resulting solution to stand a few minutes until clear. Then add, while stirring, 3 parts of Solution No. 4. The intensifier is then ready for use and the film should be treated immediately.

Six parts in all, so the working bath carries 10 g/L of silver nitrate, 20 g/L of crystalline sodium sulfite from Solution No. 2 with a further 5 g/L from Solution No. 4, 17.5 g/L of hypo and 4 g/L of Elon. This is recorded as an order of addition rather than as a ratio because the handbook's own sentence is an order: a precipitate has to be made and then dissolved before the developing agent arrives, and the same six parts combined in a different sequence would put a reducing agent into an undiluted silver nitrate solution.

Purpose

To add density to a thin transparency in proportion to the density already there. Kodak Limited’s header is “Silver intensifier for proportional intensification of positive and negative transparencies without affecting image colour and stability”.

The 1928 primer supplies the definition underneath it. Intensification is photographically the opposite of reduction, the object being to increase contrast, and it is done by the deposition of some material on the silver image. The primer names three materials in ordinary use — silver, mercury and chromium compounds — and this formula is the first of the three.

That last clause of Kodak’s header is the one worth reading twice. Without affecting image colour and stability is a claim made in a handbook that also prints a mercury intensifier, and the 1928 primer’s own verdict on mercury is that mercury-intensified images are not as stable as chromium-intensified ones. Silver added to a silver image is the one intensification that leaves the image made of what it was made of before.

Recommended uses

A thin transparency that has real detail in it. Kodak names positives and negatives on film and plate. The word that governs the whole page is proportional: the bath builds on what is there, so it rewards a negative that is thin overall and punishes one that is empty in the shadows.

Where colour and permanence must not change. This is the intensifier’s distinguishing claim and the reason it is the one still worth knowing.

Where the result must be controllable by time. Kodak’s only control is the clock — the degree of intensification depends on the time of treatment — with a ceiling of 25 minutes and no floor.

Not on an under-exposed negative. An intensifier acts on silver that is already there. Where a negative carries nothing above base plus fog there is nothing to intensify, and what comes back is a more contrasty negative with the same empty shadows.

When another formula is preferable

• In almost every case, a better negative. No part of this course currently teaches negative intensification as practice, and the course’s own position on the density-and-contrast case is that the answer is exposing and developing for the negative you want rather than repairing it afterwards. This entry publishes the formula; it does not claim a lesson has adopted it.
• Where a print rather than a negative is thin, print it differently. Intensification is a negative treatment.
• Where the simplest published route is wanted, and a sulfide bath is acceptable, the 1928 primer’s re-development intensifier: bleach in the ferricyanide-and-bromide formula used for sepia toning and blacken with sodium sulphide exactly as in print toning. The primer gives it no formula number and no quantities of its own, so it has no entry here; the two baths it names are the rehalogenating ferricyanide-bromide bleach and the sulfide bath of T-52, and both are published. It is a Level C route because of the sulfide, and it changes the image colour, which is exactly what IN-5 does not do.
• Never the historical alternatives. Kodak’s IN-1, IN-4 and IN-21 are mercury, chromium(VI) and uranium. All three are in this formulary as historical study at Level D with no procedure, and this page is not a milder version of them — it is the reason the course can discuss intensification at all without one.

Mixing

Four stocks, made separately, and a working bath assembled in one order.

1. Stock No. 1. Dissolve 60 g of silver nitrate crystals in distilled water and make up to 1000 mL. Brown bottle, per Kodak Limited’s own parenthesis. Read the silver nitrate handling SOP before the jar is opened.
2. Stock No. 2. Dissolve 120 g of crystalline sodium sulfite — or 60 g of the anhydrous salt — and make up to 1000 mL.
3. Stock No. 3. Dissolve 105 g of hypo and make up to 1000 mL.
4. Stock No. 4. Dissolve 24 g of Elon first, then 30 g of crystalline sodium sulfite (or 15 g anhydrous), and make up to 3000 mL. The Elon-first order is the handbook’s general instruction for every formula containing it, and its reason is solubility rather than oxidation: Elon dissolves readily in warm water and only slightly in a sulfite solution without alkali.

Then, and only immediately before use: one part of No. 2 slowly into one part of No. 1 with stirring; one part of No. 3 to dissolve the white precipitate that appears; stand a few minutes until clear; three parts of No. 4 with stirring. Use it at once.

⚗Why that order and no other

The order is not a convenience. Solution No. 1 is a 6 per cent w/v solution of an oxidiser and Solution No. 4 is a developing agent, which is a reducing agent by definition. Kodak’s sequence puts three interventions between them: the silver is precipitated by the sulfite, the precipitate is redissolved by the thiosulfate as a complex, and only then — into a bath that is already six-sevenths of the way to working dilution — does the developer arrive.

The silver nitrate page carries the general incompatibility that this order respects: silver nitrate against reducing agents, as an intimate mixture of solids or a concentrated encounter, is on CAMEO’s list with cases attached. The two solids never meet in this formula and the two concentrated solutions never meet either. Whether Kodak chose the order for that reason or for the photographic one it states — a clear solution that deposits silver evenly — the handbook does not say, and this page does not decide it. What it does say is: follow the order.

Kodak names “the white precipitate which appears” and does not name the compound. Neither does this page. Sulfite is a weak silver ligand and thiosulfate is a strong one, which is why the third solution clears what the second one made; the identity of the solid in between is not established anywhere in this corpus.

🧮What one plus one plus one plus three gives you

Six parts in all. Per litre of working intensifier:

60 g/L × 1/6 = 10 g per litre

Silver nitrate

120 g/L × 1/6 + 10 g/L × 3/6 = 25 g per litre

Sodium sulfite, crystalline

105 g/L × 1/6 = 17.5 g per litre

Sodium thiosulfate

8 g/L × 3/6 = 4 g per litre

Elon (metol)

Two of those numbers are worth holding. Four grams of metol per litre is an ordinary paper-developer concentration — D-72 works at about three — so the developing half of this bath is unremarkable. Ten grams of silver nitrate per litre is the half that is not: this is a developer with about 6.4 g of silver per litre dissolved in it, and every gram of it is there to end up on the negative or in the waste bottle.

The crystalline sulfite is the heptahydrate at 252.15 g/mol against the anhydrous salt’s 126.04, which is why Kodak Limited’s alternative weights are exactly half.

Scrupulously clean dishes, and the work preferably in artificial light. Both are Kodak Limited’s own sentences, and the second is a reminder that a silver-bearing developing solution is a photographic material in its own right.

Behaviour

It has half an hour to live. The mixed intensifier is stable for approximately 30 minutes at 18 °C, and the film goes in immediately. This is the shortest published working life of any bath in this formulary.

Time is the only control. The degree of intensification depends on the time of treatment, up to a ceiling of 25 minutes. There is no dilution, no temperature and no agitation regime published for the treatment itself.

No temperature is published for the bath in use. The 18 °C in the handbook attaches to the keeping statement. This entry does not extend it to the treatment, and neither should a worker: it is a statement about how long the bath lasts, not about how warm it should be.

The precipitate is a checkpoint, not a fault. If no white precipitate appears when No. 2 goes into No. 1, something is wrong with one of the two stocks. If it does not clear when No. 3 is added, the bath is not ready and Kodak’s instruction is to stand a few minutes until it does.

It is followed by a hypo bath and a wash, not by a fixer: two minutes with agitation in a plain 30 per cent w/v hypo solution, then wash thoroughly. That is three quarters of the strength of the plain hypo fixing bath in this formulary, and its job here is to clear silver the intensifier left in the gelatin rather than to fix an undeveloped halide.

Kodak publishes no capacity, and for a bath with a thirty-minute life the question hardly arises: it is mixed for the work in hand.

Image characteristics

Density rises roughly in step with the density already present. That is what proportional means in the 1928 primer’s classification, applied to the opposite operation: where a proportional reducer exactly undoes development, a proportional intensifier extends it.

Contrast rises with it. A proportional gain multiplies the difference between the dense and the thin parts.

The shadows gain least, and an empty shadow gains nothing. This is the property that decides whether the formula is any use on a given negative, and it is the reason an under-exposed negative comes back contrastier and no better.

Colour and stability are claimed to be unaffected, which is Kodak’s own header and the formula’s whole argument for existing. What is deposited is silver, on an image that was already silver.

Kodak publishes no figure for how much density it adds, at any time, on any material. The ceiling of 25 minutes is the only quantity attached to the effect, and this entry does not convert it into one.

The mechanism

Silver arrives from the solution and lands on silver that is already there.

The 1928 primer states the general principle: intensification is the deposition of some material on the silver image, and the material may be a silver compound. What this bath adds to that is a route by which silver can be carried in a developing solution without being reduced before it arrives — a sulfite precipitation followed by a thiosulfate redissolution — and a developing agent to put it down.

⚗Development that builds from outside

Ordinary development reduces silver ions that were already in the crystal the latent-image speck sits on. Physical development is the alternative: development with a solution that itself contains silver ions, which plate out onto existing specks and build the image from outside. IN-5 is a solution that contains silver ions and a developing agent, applied to an image that is already fully developed, so what it does is physical development onto a finished negative.

The half-reaction is the one every developer pays for, and the course’s metol page prints it in the same form:

Ag⁺ + e⁻ → Ag

The silver in the bath becomes silver on the image; the electron comes from the Elon

No balanced equation for the oxidation of metol is printed here, because none is in this corpus. The metol page takes the same position, and the reason is Rule 1 rather than modesty: a plausible equation for an organic oxidation is exactly the kind of thing that gets copied afterwards.

Why it should be proportional, and what the course is asserting when it says so. Kodak asserts the classing in its header and gives no reason. The reasoning available from the 1928 primer’s own statement is that the deposit forms on the existing image, so a region with twice the silver offers twice the surface for it — which would make the gain track the density. That is a reading of the primer’s sentence and not a measurement, and nothing in this corpus measures it. It is also, unusually, checkable with a step wedge and a densitometer: see Experiments.

Why the bath dies in thirty minutes. A solution containing both a silver complex and a developing agent is a solution in which the developer is reducing the silver whether or not a negative is present. What comes down in the tray instead of on the film is the same silver, wasted; that is the ordinary fate of any physical developer and it is why Kodak prints a working life rather than a shelf life.

Function of every ingredient

Silver nitrate, 60 g to the litre of Stock Solution No. 1, 10 g/L in the working bath. The silver, and the only ingredient that adds anything to the negative. Everything else in the formula exists to carry it, hold it back or put it down. Kodak Limited specifies distilled water for this stock alone, and the reason is on the substance’s own page: soluble chlorides, bromides and iodides — including those in tap water — precipitate the silver halide immediately, so a tap-water stock is a stock of unknown strength with a haze in it. More silver would deposit faster and Kodak publishes no figure for what else it would do; less would run out before 25 minutes were up. The crystals are the anhydrous salt at 169.87 g/mol, so 60 g is 60 g whatever the jar says. Its page carries the classification, the incompatibility list and the reason this formula is Level B, and there is a handling SOP for it.

Sodium sulfite, 120 g crystalline or 60 g anhydrous to the litre of Stock Solution No. 2, and again 30 g crystalline or 15 g anhydrous to the three litres of Stock Solution No. 4. The one ingredient that appears twice, doing two different jobs at two different concentrations, which is why Kodak Limited prints it as two separate stocks rather than as one. In No. 2 it is the precipitant: added slowly to the silver nitrate it throws the white precipitate the handbook requires to appear, taking the silver out of free solution before the developing agent can reach it. In No. 4 it is the preservative of an ordinary developer, at 10 g/L — the concentration a working paper developer carries, well below the solvent concentrations that give fine grain. More in No. 2 and there is more precipitate for the hypo to redissolve; less and some silver stays as a free ion in a bath that is about to receive a reducing agent. More in No. 4 and the developer keeps better and works a little differently; less and the Elon oxidises in the tray. Kodak prints both forms, as it prints every sulfite and carbonate twice, and the crystalline heptahydrate at 252.15 g/mol is exactly double the anhydrous salt at 126.04.

Sodium thiosulfate pentahydrate, 105 g to the litre of Stock Solution No. 3, 17.5 g/L in the working bath. The solvent, and here it is a ligand rather than a fixer. Its whole job is the sentence “the white precipitate which appears is then dissolved by the addition of 1 part of Solution No. 3”: it takes the silver back into solution as a complex that a developing agent can reduce gradually and evenly instead of all at once. At a quarter the strength of the plain hypo fixing bath it is well below fixing concentration, which matters, because a fixing-strength bath applied to a finished negative would start dissolving the image this formula is meant to build on. More would begin to do exactly that; less leaves an undissolved precipitate and a bath Kodak says is not ready. The crystals are the pentahydrate at 248.19 g/mol.

Metol — Kodak Limited’s ‘Elon’ — 24 g to the three litres of Stock Solution No. 4, 4 g/L in the working bath. The developing agent, and the ingredient that turns a silver-bearing solution into an intensifier. It supplies the electron that puts the dissolved silver down as metal on the existing image. The handbook’s own front matter identifies Elon as a specially purified form of monomethyl paraminophenol sulphate, also known as Metol and Genol, so this is not a proprietary substance the course cannot look up: it is the substance on the metol page under a brand name. At 4 g/L in the working bath it sits in ordinary paper-developer territory. More would reduce the dissolved silver faster, in the tray as well as on the film, and shorten the thirty minutes further; less would leave silver in the bath at the end of 25 minutes. Note there is no alkali anywhere in this formula — no carbonate, no hydroxide, no borax — which is why the Elon has to be dissolved before the sulfite when Stock No. 4 is made, and which distinguishes this bath sharply from an ordinary developer. Its page carries the skin-sensitisation statement that governs how it is handled.

Water, distilled for the silver and ordinary for the rest, to four separate make-up volumes. Three litres for Stock No. 4 and one each for the others, because three of the six parts of the working bath come from No. 4 — so the stock that is drawn on hardest is made in the largest quantity. That is a piece of practical formulation rather than chemistry, and it is the sort of thing a flattened ingredient list would hide.

Interactions

With the order of mixing, which is the strongest interaction in the formula and is dealt with under Mixing. Out of order, this is a reducing agent meeting a 6 per cent w/v oxidiser solution.

With chloride, in tap water or on a negative. Silver nitrate meets chloride as insoluble silver chloride. Distilled water for Stock No. 1, and a negative that has been washed rather than one carrying fixer.

With residual hypo in the negative. The film should be washed after fixing before it comes anywhere near a bath carrying free silver, or the silver is spent on the hypo rather than on the image.

With light. Kodak Limited says the operations should preferably take place in artificial light, and the silver nitrate page records the salt as the outstanding example of a photographic chemical decomposed by light, with solutions darkening faster than the solid.

With dirty dishes. “All dishes used must be scrupulously clean” is Kodak Limited’s own sentence and it is not housekeeping advice: a trace of developer, fixer or dust in a physically developing bath gives it somewhere to deposit silver that is not the negative.

With ammonia, which must be nowhere near it. The silver nitrate page carries the case: ammonium hydroxide and silver nitrate treated with sodium hydroxide gave a black precipitate that exploded on stirring. This formula contains no ammonia and none should be introduced to it, its bottles or its waste.

Variants

None is published, and that is unusual. Kodak Limited prints one composition, one order of mixing, one ceiling time and one keeping figure for IN-5, with no dilution, no alternative and no second version. The four alternative forms it does print are the crystalline-or-anhydrous pairs for the two sulfite lines, and those are forms of the same substance rather than variants of the formula.

The other four intensifiers on the same handbook pages are the alternatives Kodak actually offered, and none is a variant of this one: IN-1 is mercury, IN-4 is chromium(VI), IN-6 is a second chromium(VI) formula, and IN-21 is uranium. Three of the four are in this formulary as historical study with no procedure; IN-6 is not published at all, because one of its ingredients is Kodak’s own wetting agent, whose composition its maker does not disclose.

The 1928 primer’s re-development intensifier, described above under When another formula is preferable, which is not a formula but a pairing of two that already exist.

No course variant is offered. There is no quantity here the course could improve on evidence it holds, and the thing a variant would usually be for — reducing a hazard — is not available: the silver nitrate is the formula.

Safety

Level B, from silver nitrate and metol, which are the two Level B substances in it; the sulfite and the hypo are Level A. Read both pages rather than this one for the classifications, the exposure routes and the first aid, and follow the silver nitrate handling SOP, which exists precisely because this substance turns up in several places in the course.

Two hazards belong to this formula rather than to its ingredients.

The order of mixing. Adding Solution No. 4 to Solution No. 1 would put a developing agent into a 6 per cent w/v solution of an oxidiser. Kodak’s order avoids that and this page will not print a shortened version of it.

The silver in the tray at the end. A bath that started with 10 g/L of silver nitrate and has been reducing it for 25 minutes is a silver-bearing waste with metallic silver in it, and it is not a bath to tip away casually. See Waste.

Splash protection is not optional with the concentrated stock. The silver nitrate classification carries H314, causes severe skin burns and eye damage, in almost every notification. Goggles that seal, nitrile gloves, and an eyewash within reach before the bottle is opened.

Metol is a skin sensitiser, and the consequence of sensitisation is not reversible by tightening the control afterwards. Gloves for the powder and for the solution.

No hazard specific to the mixture is recorded anywhere in this corpus — not in the handbook, not on any of the four substances’ pages. That is stated as an absence of evidence rather than as evidence of absence, and it is the reason the order of addition is treated on this page as a rule rather than as a preference.

Storage

Stock No. 1 in a brown bottle, which is Kodak Limited’s only storage instruction for the formula, and made with distilled water. Silver nitrate solution darkens in light faster than the solid does, and a darkened stock has already put some of its silver where you cannot use it.

Stock No. 4 away from the light and stoppered, as any Elon-and-sulfite solution: it is a developer without an alkali, and it oxidises in air like one.

Stocks No. 2 and No. 3 as ordinary sulfite and hypo solutions.

No keeping figure is published for any of the four stocks and none is invented here. The only keeping number in the formula is for the mixed bath and it is thirty minutes.

The working bath is not stored at all. It is mixed for the negative in front of you and it is spent, one way or another, within the half hour.

Label all four bottles with the formula, the solution number, the strength and the date, and note that two of them are sulfite at two different strengths for two different jobs. Mixing up Stock No. 2 and Stock No. 4 would put a developing agent where the precipitant should go.

Incompatibilities

Ammonia, absolutely, including ammonia-based cleaners near the bench. Silver nitride.

Reducing agents, as solids or concentrated solutions, against the silver nitrate stock. Inside this formula that encounter is managed by the order of addition; outside it, keep the silver nitrate jar away from every developing agent on the shelf.

Combustible material, against the solid silver nitrate, which is an oxidiser: paper, cloth and wood loaded with it are a fire risk as they dry.

Chlorides, bromides and iodides, including those in tap water, which take the silver out of solution as a halide.

Acids, against the hypo, which they decompose to sulfur and sulfur dioxide, and against the intensified negative afterwards — Kodak’s own instruction is a plain hypo bath and a wash, not an acid fixer.

Developer, in either direction, as for every bath in the darkroom. One pair of tongs per tray.

See incompatibilities.

Waste

This is a silver-bearing waste with more silver in it than most. Ten grams of silver nitrate to the litre is about 6.4 g of silver, and a bath that has done its work still holds most of it — as unreduced complex, as metallic silver that came down in the tray rather than on the film, or both.

It gets its own labelled container. So does the two-minute hypo bath that follows the treatment, which now carries silver cleared out of the gelatin.

Silver recovery first where it is available. Of everything in this formulary this is the stream most worth recovering, and Kodak’s own guidance treats silver as the effluent parameter municipalities most often regulate.

No acid into it, which is the general rule for a thiosulfate-bearing waste.

Collect it, label it, and follow the silver-bearing waste SOP and the disposal ruling. Local regulation decides, and this course cannot tell you what it says where you are.

Troubleshooting

No white precipitate when Solution No. 2 goes into Solution No. 1. The handbook says one appears, so its absence means one of the two stocks is not what it should be — a silver nitrate stock made with tap water and already spent on chloride, or a sulfite stock that has oxidised to sulfate. Make both again.

The precipitate will not clear after Solution No. 3. Stand it a few minutes, which is Kodak’s own instruction. If it still will not clear, the hypo stock is under-strength or sulfured. Do not proceed to Solution No. 4 with a cloudy bath.

The bath went grey or threw a mirror on the dish. The silver is being reduced in the tray rather than on the film. Most likely the thirty minutes are up, or Solution No. 4 went in before the bath was clear, or the dish was not clean.

The negative gained nothing. Either the time was short, or there was nothing to build on. A proportional intensifier cannot put detail into a shadow that has none; check the negative against base plus fog before blaming the bath.

The negative gained contrast and no shadow detail. That is the formula behaving exactly as described, on a negative that was under-exposed rather than under-developed. This is not a fault to fix in the tray.

Stains or an uneven deposit. Dirty dishes, insufficient washing before the treatment, or hypo carried in from fixing. Kodak’s “scrupulously clean” is doing more work than it looks.

Everything went right and the negative dried down flatter than it looked wet. Read a step wedge rather than judging by eye; see Experiments.

Experiments

Test Kodak’s word “proportional”, which is the one claim on this page nothing in the corpus measures. Expose and develop a step wedge, read every step, intensify it, and read it again. Plot the gain in density against the original density of each step. A proportional intensifier should give a straight line through the origin; a cutting one would give a constant offset; a flattening one would bend the other way. Kodak asserts the first and publishes nothing to support it.

Map the time. Five identical strips at 2, 5, 10, 15 and 25 minutes, all from one mixed bath if it will last and from fresh baths if it will not. Kodak publishes a ceiling and no target; this is the curve that turns the ceiling into a working choice.

Watch the bath die. Mix one working bath, treat one strip immediately and an identical strip at 30, 45 and 60 minutes. The handbook’s thirty minutes at 18 °C is a number worth checking against your own bench, and the failure mode — silver going down in the tray rather than on the film — is visible.

Break the order deliberately, on paper rather than in the tray. Write out what would be in the vessel at each step if Solution No. 4 went in second instead of last, and what the silver nitrate page says about that encounter. This is the cheapest experiment on the page, and it is the one to do first.

Compare the two intensification routes the course can publish. One strip through IN-5, an identical one through the 1928 primer’s re-development route — the rehalogenating bleach followed by the sulfide bath — and both read. Kodak’s claim for IN-5 is intensification without affecting image colour; the sulfide route changes the colour by design. Whether the density curves also differ is a question neither source answers.