A plain-English guide to what the chemistry actually does, how the major processes (C-41, E-6, ECN-2, B&W, RA-4) differ, and the dilution math every home developer eventually has to learn. Pair it with the Film Chemistry Mixing Calculator when you're ready to mix.
A roll of exposed film is silver halide crystals waiting to be turned into a stable image. The chemistry kit does that in three stages. The developer reduces the exposed crystals to metallic silver, giving you a visible negative or positive. A stop bath halts that process before the unexposed grains catch up. The fixer dissolves what the developer didn’t touch, so the image won’t keep darkening every time light hits it. Color and slide processes add a few more steps (bleach, conditioner, stabilizer) but the spirit is the same.
Most of these chemicals ship as concentrates or powders. Mixing them at the wrong ratio is the single most common way home developers ruin a roll. Too little developer and your highlights die. Too much fixer in the bath and the wash takes forever while the negatives go thin. The math itself is not complicated, but it gets fiddly when you’re scaling a 1-gallon powder pack down to half a liter, or working from a datasheet that lists “1+M+N” where M and N are both decimals. The calculator handles that math for 300+ products.
The standard for color print film since 1972. Kodak Gold, Portra, Fujifilm 400H, anything you’d have run through a one-hour photo lab. Three baths in a typical home kit: developer, blix (a combined bleach-fix), and stabilizer. Runs at 38°C for the developer, with the timing tightly controlled because temperature drift shifts color balance. CineStill Cs41 and the Bellini home C-41 kit are the most common home options today.
Slide film. Mostly Fujifilm Provia and Velvia plus the new Kodak Ektachrome E100. Six baths in the full lab sequence, three or four in the simplified home kits. Costlier and less forgiving than C-41 because there’s no print stage to compensate for exposure or color shifts. Bellini Cs6 and Tetenal Colortec E-6 are the home kits people reach for.
Built for movie film. CineStill 800T, 50D, and bulk Eastman 5219 are the stocks people typically run through it. The unique step is the prebath, which strips a black anti-halation backing called remjet off the film before development. Some home shooters skip the prebath and push motion-picture stock through C-41 instead. Colors shift but the film survives.
A developer, an optional stop bath, and a fixer. Almost every brand on the market: D-76, HC-110, Rodinal, Xtol, Microphen, Pyrocat-HD, T-Max Developer, ID-11, and a dozen others. The choice between them changes grain, contrast, and acutance more than it changes the underlying chemistry. Pick whatever your favorite forum tells you to start with, then experiment.
For darkroom color printing, not film. Listed here because a few all-in-one home kits cover both ends of the process.
One part developer concentrate, thirty-one parts water. So for a liter of working solution, you’d mix about 31 mL concentrate with 969 mL water. The Film Chemistry Mixing Calculator does that math to a tenth of a milliliter.
In film-developing literature, yes. The “+” form is more common in European datasheets and the “:” form in American, but both mean one part chemistry to N parts water. The only place the difference matters is in lab notation where “1:32” can mean a one-in-thirty-two final dilution. Photographic datasheets almost always use the additive form.
Powder-based developers scale linearly. If the listed entry is for a 1-gallon (3,800 mL) pack and you have a 1-liter pack, the gram-per-liter ratio is the same. The calculator multiplies for you when you ask for a different final volume.
Some manufacturers (or some kits) don’t publish per-component mix volumes. The instructions just say “as per kit”. We mark those rather than guess, because guessing wrong wastes a roll of film. If you’ve got an official datasheet and want to fill one in, email me.
Sometimes. Standard developers like HC-110 are routinely diluted further than the bottle suggests. Dilution H (1+63) is exactly half-strength of dilution B (1+31) and roughly doubles the development time. It’s used for finer grain, stand development, and easier control over hard-to-meter scenes. The calculator handles the dilution itself; the development time you have to find from the Massive Dev Chart or a process recipe.
One-shot means mix fresh for each tank, then discard. Replenished means you reuse the working solution between rolls and add a small top-up dose of replenisher to keep concentration stable. Replenished is cheaper per roll and arguably more consistent; one-shot is foolproof. Most home kits in this dataset assume one-shot, which is why replenisher entries were removed (the math is misleading without a published replenisher schedule).
No. Photo chemistry tolerances are roughly one to two percent for amateur use. A syringe that reads to whole milliliters is fine for most working solutions, and a kitchen scale that reads to one gram is fine for most powders. The calculator displays one decimal place because rounding earlier in the cascade would compound. Round to your tool’s resolution when you actually mix.
The Film Chemistry Mixing Calculator covers 300+ developer, fixer, stop bath, stabilizer, and bleach products from Kodak, Ilford, Adox, Foma, CineStill, and more. Pick a product, tell it how much working solution you need, and it does the dilution math.
Need to look up an unfamiliar term first? The Glossary of Film Photography Terms covers 200+ entries from exposure basics to darkroom mechanics. Not ready to develop at home? Find a lab on the Where to Develop Film resource.