Part V Overview: Photographic Emulsions

Everything so far has been done with materials somebody else made. From here on you make them, and the point is not self-sufficiency. It is that a commercial emulsion is the answer to about ten questions, and until you have answered them yourself the answers are invisible. Why is a contact paper slow? Why does a warm-tone paper want a different developer? Why does one film have finer grain and less speed than another at the same price? Each is a decision somebody made at a bench, and by the end of this part you will have made the same decisions, badly at first, with your own silver.

Five emulsions, in order of difficulty

The projects are progressive, and each one adds exactly one hard thing.

1. A silver chloride contact printing paper. Silver nitrate into salted gelatin, briefly ripened, not washed, coated on watercolour paper and contact printed. The simplest complete make there is.
2. A chlorobromide paper. The same operation with a mixed halide, so that halide ratio becomes a variable you have moved yourself and measured.
3. A bromide enlarging emulsion. Two sessions, because this one is washed: precipitate, ripen, set, shred, wash in changes of ice water, remelt, finish, coat. Washing is the step that separates a printing paper from a negative material.
4. Glass dry plates and a lantern slide. Cutting, cleaning and coating glass, which is unforgiving about level and about dust, and which gives you plates for the camera you build in Part VI.
5. A designed emulsion, and an orthochromatic make. A dye goes into the emulsion and the material stops being colour-blind — and the safelight you may work under changes as a consequence.

Before any of them you build a coating station and coat a bought liquid emulsion on it, so your first coating failure is not also your first emulsion failure.

!The fifth project is not what it was originally designed to be, and here is why

The plan was a double-jet, sulfur-and-gold, dye-sensitised, stabilised iodobromide emulsion. The research could not support it, and the course narrowed the project rather than inventing the missing parts. Nobody has published a domestic double-jet procedure at any tier this course can reach; no published home formula performs a measured thiosulfate digestion; the only tested gold dose sits inside an ammoniacal make, which this part excludes; and no source gives a dose for benzotriazole or a tetraazaindene in an emulsion, so a bromide restrainer with two published doses takes their place.

Project 5 is therefore two things: a design exercise in which you specify the advanced emulsion on paper from published ranges and defend your choices, and a make of the orthochromatic emulsion that is sourced and has demonstrably been made. A smaller promise, and one the evidence can keep.

What you will have at the end

A working coating station; five batch records carrying your own measurements; a lantern slide; dry plates ready for Part VI; a diagnosed set of coating defects you produced deliberately; and one hand-coated portfolio print.

The theory pages, and why they come first

Four lessons explain what the projects do. Gelatin is not a glue but a peptiser, a growth restrainer, a halogen acceptor and, by accident, the original source of the sulfur that sensitises an emulsion. Precipitation, nucleation and growth is where the number of crystals and their size are decided, in the first seconds and the following hour. Washing, digestion and sensitisation is why an emulsion is washed at all and how a few milligrams multiply its speed. Coating, drying and hardening is the part everyone underestimates.

Safety, in one paragraph

Silver nitrate at gram scale, hot gelatin at 40 to 70 °C, and a dye and a hardener in milligram quantities: every project here is Level A or B, and none of them is Level C. What is kept out is as informative as what is in. Ammonia is excluded, which means working hotter and slower than the historical formulas do, and the pages say so rather than leaving you to wonder why. Cadmium and mercury are excluded at any level. Formaldehyde is excluded — and the striking thing is that the emulsion literature threw it out first, on its own grounds: Wall in 1929 and Duffin in 1966 both rejected it independently because it causes fog on keeping, and the toxicology arrived second. That ordering matters: this is not a modern squeamishness the old hands did not share. They shared it.

!Equipment used before it is built

As in Part IV, this part assumes a darkenable room, a bought or improvised safelight and a set of trays, none yet engineered. Part XVI owns the room, the LED safelight and the fog test; until then the acceptance test is Station 4 of the latent image made visible. Contact printing here is a glass-and-board sandwich under a weight, not the sprung frame Part XVI builds. And the bromide enlarging emulsion is speed-tested by contact printing, because no enlarger has been built yet. The enlarger arrives in Part XVI, and Part XIX’s critique assignment will accept a sheet you coated here among the prints you bring to it — but no page sets making the first enlargement on your own paper as a task, and this overview said one did until 8 September 2026. If you want that print, carry this part’s batch record and contact-tested speed forward and make it yourself once the enlarger is commissioned; nothing later in the course will ask you for it.

✦Two routes for people who need them

If silver nitrate is not obtainable where you are, or you would rather not handle it, the commercial-emulsion practice run carries the coating, drying, defect and portfolio work on a bought liquid emulsion: you lose the makes and keep everything else. The coating station also has a no-woodworking version built from plate glass, tape and putty. Neither is a lesser route.

Alternative route

This overview declares a darkroom because every practical page beneath it does, so the routes belong here rather than being discovered on page four.

No silver nitrate, or no wish to handle it. Take the commercial-emulsion route, entered at coating your first emulsion. You keep the coating, the drying, the hardening ruling, the step-wedge sensitometry, the defect work, the plates Part VI exposes and the hand-coated portfolio print; you lose the five makes and the batch-to-batch chemistry that goes with them. Where a later project asks you to change a variable in the emulsion, change one in the coating instead.

No woodworking, or no bench. The coating station has a build with no cut timber in it at all, made from plate glass, tape and epoxy putty: build an emulsion coating station carries both versions.

No room that can be made dark. This is the one requirement of Part V that has no substitute, and it is worth saying plainly rather than leaving a reader to work through five projects before finding out. Bought emulsion is as light-sensitive as emulsion you make, so the commercial route does not avoid it. What can be done in daylight is every part of coating that is fluid mechanics rather than photography — levelling, viscosity, temperature, coating weight, drying, setting, hardening and the keeping test, all on plain gelatin with no silver in it, as coating, drying and hardening sets out. That is most of the craft of this part. It is not the whole of it.

What you need first

All of Part IV, whose crystals, latent image, grain and spectral sensitivity are assumed here and not re-derived. From Part II, silver nitrate handling and chemical waste and silver waste. From Part III, solubility and precipitation, complex formation and diffusion and osmosis. And a step wedge: this course has found no published speed figure for any homemade emulsion at any tier, so every number in your batch record will be yours.

Part5 of 28Level3 — AdvancedPages13Estimated time30.5 hoursHighest safety levelLevel B

✱10 of 13 pages in this part need a darkroom, a UV source or mains-powered equipment, marked below. Each says what can be improvised and, where one exists, gives an alternative route.

0 / 13 lessons in this part completed

• LessonGelatin, the Photographic Binder60 min
• LessonPrecipitation, Nucleation and Crystal Growth75 min
• LessonWashing, Digestion and Sensitisation60 min
• LessonCoating, Drying and Hardening✱ Darkroom60 min
• BuildBuild an Emulsion Coating StationA✱ Darkroom120 min
• LabLab: Coating Your First EmulsionA✱ Darkroom150 min
• LabProject 1: A Silver Chloride Contact Printing EmulsionB✱ Darkroom180 min
• LabProject 2: A Chlorobromide Paper EmulsionB✱ Darkroom180 min
• LabProject 3: A Bromide Enlarging EmulsionB✱ Darkroom240 min
• LabProject 4: Coating Glass Dry Plates and a Lantern SlideB✱ Darkroom180 min
• LabProject 5: Designing an Emulsion, and Making the One We Can SourceB✱ Darkroom300 min
• Break/fixBreak/Fix: Emulsion Coating DefectsA✱ Darkroom75 min
• AssignmentAssignment: The Hand-Coated PrintA✱ Darkroom150 min