Trumm's bromide paper emulsion

Three solutions, two timed hours at two temperatures, an apparatus specification for the addition, twelve changes of wash water and a made-up weight. Nothing else in this corpus is published in this much detail, which is why this formula is the one Part V asks a student to read and scale rather than the one it asks them to make.

Solution A — the salted gelatin, and the crock the emulsion is made in

Ingredient	Quantity	Form the source specifies
Potassium bromide	190 g
Potassium iodide	2.5 g
Gelatin	350 g	swollen in the bromide and iodide solution for half an hour before any heat
Water	4000 mL, added	Baker states the water as an amount. The only made-up figure in the formula is the 16,000 g of finished emulsion, which is a weight rather than a volume and is recorded in the combination below.
Added to the working bath, not to the stock
Chrome alum	150 mL of a 5% solution	in the finals, when the washed noodles are remelted and made up to 16,000 g
Ethanol	1000 mL	in the finals, when the washed noodles are remelted and made up to 16,000 g — printed as spirit; part of it is the solvent for the phenol this entry omits
The gelatin is allowed to swell in the solution of bromide and iodide for half an hour and is then dissolved by heating the crock to 49 °C (120 °F). The finals are attached to this solution because A is the crock that becomes the emulsion: B and C go into it, both digestions happen in it, and the finals go into what it has become after washing.

Solution B — the silver

Ingredient	Quantity	Form the source specifies
Silver nitrate	250 g
Water	2000 mL, added	at 49 °C; Distilled, and heated to 49 °C (120 °F), the same temperature as the crock it goes into.

Solution C — the second gelatin

Ingredient	Quantity	Form the source specifies
Gelatin	600 g
Water	2000 mL, added	at 60 °C; Added at 60 °C (140 °F), the temperature the emulsion is already being held at.

Mixed in this order — the whole make, in the order the source gives it

1. Start with the whole of Solution A — swollen half an hour, then dissolved by heating the crock to 49 °C
2. Then add the whole of Solution B — at 49 °C, poured through a fine jet near one edge of the crock, with room to stir
3. Then add the whole of Solution C — at 60 °C, after the first hour of digestion

Solution B, heated to 120 °F, is added to A through a funnel with a fairly fine jet mounted near one edge so that there is room for stirring. The emulsion is then further heated to 140 °F on a water bath and maintained there for one hour. At the end of the hour solution C, also at 140 °F, is added, and a further one hour's digestion is given. The emulsion is then poured out to set in a cold crock placed in ice water and stirred slowly until gelling begins, broken into noodles and washed in about twelve changes of five minutes each. The washed noodles are put into a tared crock, remelted and made up, inclusive of finals, to a weight of 16,000 g.

The jet is part of the formula. Baker specifies a plain or separatory funnel with a one or two inch length of barometer tubing of about 4 mm bore, attached by the shortest possible piece of rubber tubing and mounted so that the jet is near one edge of the crock. That is a controlled addition rate written as apparatus, and it is the only rate control the formula has. The made-up figure is a weight, 16,000 g inclusive of the finals, made up in a tared crock; the schema's make-up field holds millilitres, so it is recorded here rather than printed as though it were sixteen litres.

Purpose

To make a bromide enlarging paper — a washed iodobromide emulsion fast enough to be printed under an enlarger rather than by contact. Wall’s division of the classes is the clearest statement of what that means in practice: bromide papers are always washed emulsions, the gaslight papers usually unwashed, and the wash is what makes the speed usable.

The formula sits at the far end of Part V’s halide series. A pure chloride paper prints by contact under a lamp; a chloride-rich chlorobromide is a slow gaslight paper; this is the one you could put in an easel.

And it is the formula this part reads rather than performs. What Part V’s third project actually makes is a domestic-scale plain-silver iodobromide plate emulsion by a modern practitioner, because somebody has demonstrably made that one. This page is where the formula that is actually a paper lives, with the arithmetic that lets it be scaled and compared.

Recommended uses

As the design object for a scaling exercise. Every ratio in it survives division: halide to silver, gelatin to silver, iodide fraction, hardener to gelatin. Nothing else does. Working out what a one-hundredth batch would be, and what the arithmetic quietly fails to carry, is the exercise.

As the reference for what a complete emulsion formula looks like. Compare it with any modern recipe and the differences are instructive: the modern ones tend to omit the wash endpoint, the finals, or both.

As the source of the coating-weight arithmetic Part V uses throughout. Baker’s “one litre should coat sixty to eighty square feet” is the only trade coating rate in the corpus, and it converts into a target a hand coater can measure against.

As an enlarging paper, if you make it. Nobody the course can name has, and the honest position is that this is a formula with commercial authority and no modern reproduction.

When another formula is preferable

• When you want a make somebody has tested at domestic scale, the plain-silver iodobromide plate emulsion that the bromide project performs. It is a plate rather than a paper, and the course says so wherever it appears.
• When you want a contact printing paper, the chloride contact emulsion, which is faster to make and needs no wash.
• When you want warm tones, a chloride-rich emulsion such as Wall’s soft-working gaslight paper. More bromide makes warm tones harder to reach.
• When the emulsion must keep, no formula in this part is a good answer, and this one is published with a bacteriocide the course removes. See Storage.
• When you have no way to wash noodles, this formula is out of reach: twelve changes of five minutes is not optional in a bromide paper, and it is the step the unwashed formulas exist to avoid.

Mixing

One crock, three additions, two hours of heat, a set, a wash and a make-up by weight.

1. Swell. 190 g of potassium bromide and 2.5 g of potassium iodide in 4000 cm³ of water, then 350 g of gelatin left to swell in that solution for half an hour.
2. Melt. Heat the crock to 49 °C (120 °F) to dissolve the gelatin.
3. Emulsify. 250 g of silver nitrate in 2000 cm³ of distilled water, heated to the same temperature, poured in through a fine jet — Baker specifies a funnel fitted with an inch or two of 4 mm bore tubing, mounted near one edge so that there is room to stir.
4. First digestion. Raise to 60 °C (140 °F) on a water bath and hold for one hour.
5. Second gelatin. 600 g of gelatin in 2000 cm³ of water, also at 60 °C, added at the end of that hour.
6. Second digestion. A further one hour at 60 °C.
7. Set. Pour into a cold crock standing in ice water and stir slowly until gelling begins.
8. Wash. Break into noodles and wash in about twelve changes of five minutes each.
9. Make up. Washed noodles into a tared crock, remelted, and made up inclusive of the finals to 16,000 g.
10. Finals. 150 cm³ of a 5 per cent chrome alum solution and 1000 cm³ of spirit. Baker’s third final, 10 g of phenol, is not printed here — see the note below.

☠The phenol is in the published finals and is not in this course's version

Trumm’s finals carry 10 g of phenol per 16 kg, dissolved in part of the spirit, as a bacteriocide.

This course omits it and states the omission rather than editing the formula quietly. Phenol is not a domestic reagent, Rule 5 keeps it out of a Level B procedure, and the chemical encyclopaedia carries no entry for it, so there is no page this course could send you to before you weighed it.

What the omission costs: the emulsion’s resistance to bacteria and mould in storage. An emulsion is a warm nutrient broth and a commercial batch had to survive weeks in a tank. The replacements are small batches, refrigeration below 5 °C, and using the material rather than keeping it.

Do not substitute another bacteriocide. The corpus holds a class list — thymol, p-chloro-m-cresol, the halogenophenols, at around 0.1 per cent of the gelatin weight — and no worked formula for any of them in an emulsion. Choosing one would be inventing a procedure, which is the thing Rule 6 exists to prevent.

🧮Trumm's formula in seven numbers

250 g AgNO₃ ÷ 169.87 = 1.472 mol

Silver

190 ÷ 119.00 = 1.597 mol Br⁻; 2.5 ÷ 166.00 = 0.0151 mol I⁻; total 1.612 mol

Halide

1.612 ÷ 1.472 − 1 = 9.5 mol per cent

Halide excess

0.0151 ÷ 1.612 = 0.9 per cent of the halide, 1.0 per cent of the silver

Iodide

950 g ÷ 1.472 = 645 g per mole

Gelatin per mole of silver

150 mL × 5 % = 7.5 g; 7.5 ÷ 950 = 0.79 per cent

Hardener against gelatin

250 g in 16,000 g = 15.6 g of silver nitrate per kilogram

Silver concentration

Four of those are worth an argument.

The excess. Nine and a half per cent is an order of magnitude below the forty-five per cent excess a domestic plate emulsion runs at, and the difference is the difference between a paper and a plate: a paper does not want the grain a large bromide excess ripens up to.

The gelatin. Six hundred and forty-five grams per mole of silver is a paper’s gelatin load — two and a half times a plate emulsion’s — and it is why a paper coats and dries as it does.

The hardener. Against the gelatin rather than against the emulsion, which is Wall’s rule and follows from the mechanism, 7.5 g in 950 g is 0.79 per cent. Duffin’s general band is 0.5 to 2 per cent, and this sits comfortably inside it, alongside Baker’s own 0.625 per cent elsewhere and Wall’s 0.33 to 0.40. Expressed as a fraction of the emulsion — 0.047 per cent — the number is meaningless and does not survive scaling.

The silver concentration. 15.6 g per kilogram is at the very bottom of Baker’s own stated band of fifteen to twenty-five grams per litre for paper emulsions, against forty to fifty for negative emulsions. The formula and the general statement come from the same author on facing pages, and they agree.

Behaviour

It is a washed emulsion, and that is the whole difference from the gaslight papers. Twelve changes of five minutes takes out the potassium nitrate the precipitation made and most of the halide excess, and what is left is an emulsion whose speed is not being held down by its own by-products.

No source in this corpus gives a wash endpoint for this formula. Baker gives a number of changes and no test. The only endpoint criterion anywhere in the corpus is a modern practitioner’s, arrived at by measuring the pH of the wash water: her curves fell identically from 10 to 7.8 over two separate trials, and her rule is to reach a pH between 7 and 8 and to avoid overwashing. That is a Tier 2 method from a different formula, and it is offered here as the only test there is rather than as Baker’s.

Two digestions, an hour each, and no chemical sensitiser. The whole of the sensitisation is what the gelatin brings and what two hours at 60 °C do with it. In an active gelatin of the period that is about a hundred parts per million of active sulfur; in a modern inert photographic gelatin it is one to two. That is the largest single reason a modern reproduction of this formula would not behave as Trumm’s did, and no correction for it exists that this course can publish.

The addition rate is written as apparatus rather than as a time. A 4 mm jet near the edge of a stirred crock is a rate; a stopwatch would have been another way of saying it, and Baker chose the one that reproduces.

🧮The coating weight the trade actually used

Baker gives one litre of emulsion as covering sixty to eighty square feet of paper. Turn that into a coating weight for this emulsion.

1.457 mol AgBr × 187.77 + 0.0151 mol AgI × 234.77 ≈ 277 g

Silver halide in the make

277 g ÷ 16 kg ≈ 17 g per litre

Per kilogram of made-up emulsion

60 × 9.29 = 557 dm², so 17 g ÷ 557 = 31 mg/dm²

Sixty square feet

80 × 9.29 = 743 dm², so 17 g ÷ 743 = 23 mg/dm²

Eighty square feet

Twenty-three to thirty-one milligrams of silver halide per square decimetre is what the trade laid down on a bromide paper. Baker’s separate figure for chloride and chlorobromide plates is not more than 25 to 40 mg/dm², so the two are the same order.

Hold that number against a hand coat. A domestic chloride paper coated at 50 mL to an 11 × 15 inch sheet lays down something like three times as much, and this is the arithmetic that makes “coat it thin” into a target rather than an exhortation.

Image characteristics

Baker states none for this formula, and that absence is worth naming: the most completely published make in the corpus gives quantities, temperatures, times and apparatus, and says nothing about how the paper looks.

What can be said comes from the class rather than from the formula. Wall’s general rule is that the more bromide an emulsion carries against chloride, the faster it is, the longer its scale of gradation, and the less easily warm tones are obtained. A bromide enlarging paper is therefore the cold, long-scaled end of the series this part works through.

Image colour is the developer’s business, on the best evidence in the corpus. Wall’s own controlled series across the whole halide range, developed in one developer, produced the same colour every time, and he concluded that the rate of silver deposition decides it. A bromide paper is harder to make warm not because its halide forbids it but because it develops fast.

Grain should be fine at this halide excess, which is one of the things a 9.5 per cent excess buys: not much bromide is left over to ripen the crystals up.

The one measurable criterion the source does give is a fog limit, and it is a good one: on a trial coating on glass, fog should not exceed 0.02 density. That is a number a densitometer settles.

The mechanism

A double decomposition run slowly into a warm, gelatin-protected vessel, twice heated.

AgNO₃ + KBr → AgBr + KNO₃

The bromide, 99 per cent of the halide

AgNO₃ + KI → AgI + KNO₃

The iodide, one per cent, and taken up first

The iodide goes in first even though it is added at the same time. Silver iodide is very much less soluble than silver bromide, so as the silver arrives it is the iodide that is captured preferentially. What forms is a mixed crystal with iodide concentrated towards its core, and one mole per cent of iodide changes the crystal’s behaviour out of all proportion to its share: it distorts the lattice, and the defects that follow are where a latent image is built.

Why the gelatin arrives in two portions. The 350 g in Solution A is present while the crystals form, so it is doing colloid work: it keeps the growing crystals apart and it is thin enough not to slow the diffusion that lets them grow. The 600 g in Solution C arrives after an hour of ripening, when growth is finished and what the emulsion needs is body — enough gelatin to set firm, to noodle, to survive washing and to coat. Adding all 950 g at the start would have made a viscous crock during the one operation where diffusion decides the result.

The two hours at 60 °C are Ostwald ripening, with the modest halide excess as the only solvent. Small crystals dissolve and redeposit on large ones; the mean size climbs and the distribution broadens. There is no ammonia in this formula, so the temperature and the time are doing all of it, which is why both are long.

The wash stops it. Once the excess halide is gone the ripening has no solvent, and the emulsion is fixed at the grain distribution the digestion gave it. Setting the emulsion in ice water before shredding is the other half of that: Wall records the same practice of pouring bromide emulsions into ice-cold pans immediately after digestion, precisely to stop the ripening.

The finals harden and help the coating, and the hardener goes in last for the reason Duffin gives — chrome alum’s reaction is rapid, and it belongs in the molten emulsion immediately before coating rather than earlier.

Function of every ingredient

Silver nitrate, 250 g in 2000 cm³ of distilled water, at 49 °C. The silver, 1.472 moles, and the cost of the batch. Two things about how it arrives are part of the formula rather than of the procedure: it is at the same temperature as the crock, so the addition does not chill the vessel and set the gelatin locally, and it arrives through a 4 mm jet near one edge of a stirred crock, which is a rate control. More silver against this halide would eat the 9.5 per cent excess and leave unprecipitated silver nitrate in a washed emulsion, which fogs; less thins the coating weight towards the poor maximum black Baker warns is misdiagnosed. Distilled water is specified for the silver and not for the rest, which is Baker’s own distinction and worth keeping.

Potassium bromide, 190 g. The halide, 1.597 moles, and 99 per cent of the halide present. The excess over the silver is 9.5 mole per cent and that number is the formula’s character: enough to drive the precipitation to completion and to act as the ripening solvent for two hours, and not enough to grow the coarse grain a plate emulsion wants. More bromide ripens the grain up, raises speed and coarsens the paper; less risks unprecipitated silver. It comes as hard pellets that dissolve slowly and incompletely, and an undissolved piece during precipitation shows in the finished print as a black speck — grind it and store it airtight.

Potassium iodide, 2.5 g. One mole per cent of the silver, which is at the very bottom of the 1.0 to 8.0 per cent range the manufacturing literature gives for iodide in a bromide emulsion. It is taken up preferentially because silver iodide is the least soluble of the three silver halides, so it concentrates in the crystal cores and distorts the lattice; the practical return is speed and cleaner highlights. More iodide raises speed further up to a point and then costs it, and makes fixing slower, because silver iodide is the hardest of the halides for a fixer to remove; less takes the emulsion towards a plain bromide. At 2.5 g in a 16 kg make it is the smallest weight in the formula and it is not a rounding.

Gelatin, 350 g in A and 600 g in C — 645 g per mole of silver in all. Two ingredients with one name. The first portion is the protective colloid, present while the crystals form, thin enough to let them grow and thick enough to keep them apart. The second is the binder, added after the first digestion, and its job is body: setting firm enough to shred into noodles, surviving twelve changes of wash water, and coating. More of the first portion makes a finer grain and a slower emulsion; more of the second thickens the melt and the coat. And the type is the largest uncontrolled variable in the whole formula: Trumm assumed an active gelatin at around a hundred parts per million of active sulfur, and a modern inert photographic gelatin carries one to two, so an inert gelatin will give a cleaner and markedly slower emulsion than Baker’s page describes. That is a difference the course can name and cannot correct.

Chrome alum, 150 cm³ of a five per cent solution — 7.5 g — in the finals. The hardener, at 0.79 per cent of the dry gelatin, which is the figure to quote and to scale by, since the dose depends on the total gelatin and not on the bulk of the emulsion. It goes into the made-up emulsion rather than into the mix, which is where the manufacturing literature also puts it, and it is added slowly to a moving emulsion, because too rapid an addition coagulates the batch through a temporary local excess. More hardening makes the layer harder for developer and fixer to penetrate, and on a thick hand coat that shows up as a patch that darkens weeks later; less leaves a layer that frills. Note that it is delivered as a five per cent stock rather than as a weighed solid, which is how a dose of this size is handled at any scale. It is chromium(III), and the chromium policy holds the distinction from dichromate once for the whole course.

Ethanol, 1000 cm³ of spirit in the finals — 6.25 per cent of the made-up emulsion. The coating and setting aid: it lowers the surface tension of the melt so it wets and flows on a sized paper, and it speeds setting and drying. That is a great deal more alcohol than a plate emulsion carries, and the difference is the paper. In the published formula it has a second job, as the solvent that dissolves the phenol; with the phenol removed it has only the first. More would begin to affect the setting of the gelatin; less costs coating quality.

Water, 4000 cm³ in A, 2000 cm³ in B, 2000 cm³ in C, and then enough to make 16,000 g. Not a filler at any of the four points. A’s water sets the concentration the crystals form at; B’s sets how fast the silver arrives per unit of stirring; C’s carries the bulk gelatin in at temperature; and the make-up sets the coating weight, which is what a made-up weight actually is. Baker states three of them as amounts and only the last as a make-up, and this page keeps his distinction.

Phenol, 10 g, which is in Baker’s formula and not in the list above. Its function is the reason to name it rather than delete it: it is a bacteriocide, protecting a warm gelatin emulsion against bacteria and mould through weeks in a tank and months on a shelf. The course removes it under Rule 5 and accepts the cost, which is that this emulsion has no biological protection at all. See Storage for what replaces it, and note that no substitution is offered because no worked formula for one exists in this corpus.

Interactions

With the gelatin’s own sulfur, which is the emulsion’s only chemical sensitiser. Two hours at 60 °C is a digestion, and what it digests is whatever the gelatin brought.

With the wash water’s temperature. Noodles washed in warm water melt; noodles washed in ice water stay noodles. The wash is done cold and the emulsion is set hard before it is shredded.

With overwashing, which is a real failure and not a theoretical one. Take out too much of the halide excess and the emulsion loses the ion that was stabilising it. The only published endpoint anywhere in the corpus is a pH between 7 and 8 in the wash water, and it comes from a different formula.

With the fixer, through the iodide. Silver iodide is much harder to fix out than silver bromide, and a paper carrying iodide needs its fixing time checked rather than assumed.

With sulfite, at the finals. Chrome alum loses its hardening power in the presence of sulfite. There is none in this formula, and there is plenty in a fixer, so the finals bottle and the fixing tray do not share glassware.

With bacteria and mould, which is now an open interaction rather than a closed one, because the protection the formula was published with has been removed.

Variants

The one-hundredth scaling, which is the course’s arithmetic and not Baker’s. Silver nitrate 2.5 g, potassium bromide 1.9 g, potassium iodide 0.025 g — deliverable as 2.5 mL of a 1 per cent solution — gelatin 3.5 g in 40 cm³ for A, 20 cm³ of water for B, gelatin 6 g in 20 cm³ for C, made up to 160 g with 1.5 cm³ of 5 per cent chrome alum and 10 cm³ of spirit. Scaling preserves every ratio and none of the reactor: a 4 mm jet into a stirred crock and a syringe into a cup are not the same addition, and addition rate is what decides how many crystals form. The bromide project sets it out with its working.

Baker’s matt-surface option, printed with the formula: 200 g of rice starch ground up in 1000 to 1500 cm³ of water, stirred in prior to filtering, leaving out an equivalent quantity of water when making up. It is a physical rather than a chemical modification — a scattering filler in the layer — and the course records it without adopting it, since rice starch has no entry in this encyclopaedia.

Baker’s surfactant note, also printed with the formula: an alcoholic solution of saponin or extract of quillaia bark is frequently added to give better coatings. No quantity is given, so there is nothing to print, and neither substance has an entry here. It is a named absence.

The ammoniacal bromide paper Baker prints immediately afterwards, attributed to E. J. Wall, and the same formula Wall prints in his own book. Two Tier 1 sources agreeing, one citing the other, which is a useful thing to have seen. It is ammoniacal, and Part V excludes ammoniacal makes at Level B, so the course does not carry it.

A sulfur digestion is not offered as a variant, and the reason is the one this entry has to keep repeating: the published record gives a range — 25 to 150 parts per million of thiosulfate in the gelatin, which at 200 g of gelatin per mole works out at 5 to 30 mg per mole of silver — and no formula anywhere in the corpus performs one as a step. A range is enough to teach the chemistry and to design an experiment. It is not enough to print a dose inside a procedure and call it published practice.

Safety

Level B after one substitution, and the substitution is a subtraction. With the phenol out, what remains is silver nitrate at scale, chrome alum in the finals, alcohol, and two hours of a 60 °C water bath.

Silver nitrate sets the level: Danger, with the oxidiser, corrosive, health-hazard and environmental pictograms. At Baker’s own scale this formula puts a quarter of a kilogram of it on a bench, which is another reason the course scales before it makes.

Chrome alum is Warning, GHS07, with skin and eye irritation and possible respiratory irritation notified, and no sensitisation or carcinogenicity statement. Deliver it as a five per cent stock made once, as the formula itself does, and the powder is weighed once in the life of the bottle.

Phenol is the reason this page carries a substitution note at all, and the substitution is that it is not used. That decision is Rule 5’s and it is recorded rather than hidden.

The heat is a real hazard at this scale. Sixteen kilograms of emulsion at 60 °C in a crock is a scalding hazard of a different order from a cup in a saucepan, and so is a crock of ice water being poured into.

The alcohol goes in beside a warm water bath, which is the standing fire question on an emulsion bench.

No ammonia, no cadmium, no mercury, no chromium(VI).

Storage

The emulsion, in the published formula: best set off and remelted the next day or when required for coating. That is the only handling instruction Baker gives and it is not a keeping figure.

The emulsion, with the phenol removed: unprotected. This is the honest cost of the omission and it changes the storage advice rather than leaving it alone. Make small batches. Refrigerate below 5 °C. Use the material rather than keeping it, and treat a musty smell or a surface film as the end of that batch.

Do not substitute a bacteriocide, for the reason given under Mixing: a class list is not a dose.

The coated paper, dried in the dark and stored lightproof. The only keeping criterion in the corpus is Baker’s own trial-coating fog limit of 0.02 density, and his industrial oven test elsewhere; neither is a shelf life for a drawer.

The dry chemicals by their own entries: silver nitrate dark and dry; potassium bromide airtight and ground; potassium iodide dark, because an iodide yellows as it oxidises; chrome alum dry and away from sulfite.

The five per cent chrome alum stock keeps its hardening power indefinitely as a plain aqueous solution on Kodak’s account, which is why making it once is the sensible route.

Incompatibilities

Silver nitrate with organic matter, skin, dust and bare metal. See incompatibilities.

Thiosulfate anywhere near the make, which dissolves silver halide. Separate glassware for the emulsion and the fixer.

Sulfite with the chrome alum stock, which destroys its hardening power.

Warm water with the noodles, which undoes the wash by melting what is being washed.

Iron and rust, which put reduced silver where it is not wanted; a corroding whisk is the classic source.

Bacteria and mould, which this formula no longer resists.

Waste

Two streams and a large one. The wash water is the bulk: twelve changes of five minutes on a 16 kg make is a great deal of water carrying potassium nitrate, the halide excess and whatever silver did not precipitate. The processing baths carry the rest of the silver, mostly in the fixer.

Collect the silver-bearing streams and label them, per the disposal ruling and the general chemical waste SOP. No source in this corpus characterises the composition of an emulsion wash water, which is a real gap and is recorded as one.

Chromium(III) is present in the finals and therefore downstream of them — the coating vessel, the processing baths, the wash. Seven and a half grams in a 16 kg make is a small fraction and it is still a chromium stream: see the chromium(III) rinse route.

Local regulation decides, and this course states the chemistry without computing a threshold.

Troubleshooting

Black specks in the print. Undissolved potassium bromide during the precipitation, or rust. The bromide comes as hard pellets; grind it, dissolve it fully, and check the crock before the silver goes in.

The emulsion will not shred, or the noodles fuse in the wash. The set was not hard enough or the wash water is too warm. Set in ice water, stir slowly only until gelling begins, and wash cold.

The emulsion is flat and slow. The most likely cause is one the formula cannot fix: a modern inert gelatin brings one to two parts per million of active sulfur where Trumm’s active gelatin brought about a hundred, and two hours of digestion cannot make sensitivity out of sulfur that is not there. Record it rather than compensating by guesswork.

High fog. Check the digestion first, then the wash. Baker’s own criterion is on hand: coat a trial on glass and read it, and a batch above 0.02 density of fog is a batch to reject rather than to print with.

Weak maximum black. Measure the coating weight before blaming anything else, because Baker’s warning is explicit that too thin a coating is mistaken for it.

The paper frills or the layer lifts. At 0.79 per cent of the gelatin the hardener is mid-band, so suspect the coating weight and the processing temperature first. The remedy that does not alter the formula is an acid hardening fixer such as F-5.

The emulsion coagulated when the finals went in. The chrome alum went in too fast or into a still melt. Dilute stock, slow addition, moving emulsion.

It has gone mouldy or smells sour. The bacteriocide is not there. That is the stated cost of the omission and the answer is smaller batches, not a substitution.

Experiments

Scale it and then find what the scaling lost. Make the one-hundredth batch and record the addition time. Baker’s 4 mm jet into a large crock delivers 2000 cm³ over some number of minutes; your syringe delivers 20 cm³ over some other number. Compute both as millilitres per minute per litre of receiving solution, and you will have measured the one ratio that scaling does not preserve.

Put a paper against a plate at one silver charge. This formula at one hundredth carries 2.5 g of silver nitrate; the domestic plate emulsion carries 5 g. Coat both onto paper at the same computed coating weight and read them on the same wedge. A 9.5 per cent halide excess against a 45 per cent one, and 645 g of gelatin per mole against 238, are the two variables that separate a paper from a plate.

Find the wash endpoint for yourself. Measure the pH of the wash water at every change through all twelve. Baker gives a number of changes and no test; the only endpoint criterion in the corpus is a pH between 7 and 8 from a different formula and a different maker. Two runs will tell you whether your curve repeats, which is the thing that makes an endpoint usable.

Coat at the trade’s weight. Compute the volume that puts 23 to 31 mg of silver halide per square decimetre on your sheet, coat one at that and one at whatever your rod naturally lays down, and read both for maximum black. This is the cheapest way to find out whether your coating is the fault you have been blaming on the emulsion.

Test the hardener against the gelatin. Batches at 0.4, 0.79 and 1.6 per cent of the dry gelatin, everything else held, each fixed in a plain hypo bath and read for frilling and for how long the fix takes to clear. Duffin’s warning is that excessive hardening interferes with penetration; this is what it looks like on paper.

Make the phenol’s absence visible. Split a batch, refrigerate half and leave half at room temperature in the dark, and look at both after a week. The course removed an ingredient and stated the cost; this is how you find out what the cost is in your kitchen.