Developers: what the bottle does and what the dilution changes

A developer has three jobs: turn exposed silver halide into metallic silver, do it at a rate you can time, and leave the unexposed halide alone so that fog stays low. Everything else, grain, sharpness, speed, the shape of the curve, is a trade between those jobs, and the dilution is the knob. Here are the families, what they do, and the figures from the sheets.

The general-purpose standard: D-76 and ID-11

Kodak's D-76 and Ilford's ID-11 are the reference developers; Ilford's own HP5 Plus table gives both the same 7½ minutes at full strength ⁵. Kodak describes D-76 as giving full emulsion speed, excellent shadow detail and fine grain, and says that diluted 1:1 it gives greater sharpness with a slight increase in graininess ¹. That sentence is the whole philosophy of dilution: more water, less solvent action on the grain edges, crisper edges and a touch more visible grain. The 1:1 solution is one-shot. Kodak says mix it just before use, discard it after the batch, and give one 135-36 roll at least 473 ml of it; in a 237 ml tank, add 10 per cent to the time ¹. For Tri-X 400 at 20 °C in a small tank Kodak's October 2021 sheet gives 6¾ minutes at full strength and 9¾ at 1:1 ⁴.

XTOL: the ascorbate alternative

XTOL is Kodak's two-part powder built around vitamin C chemistry rather than hydroquinone. Kodak's list of claims includes excellent emulsion speed with normal and push processing, enhanced sharpness especially at 1:1, and 10 per cent greater enlargeability at equivalent grain ³. Full strength it has a stated capacity of about 15 rolls per litre with time compensation, and six months' life in full, tightly closed bottles ³; the 1:1 dilution, like D-76's, is use-once ³. Tri-X 400 at 20 °C: 7 minutes stock, 9 at 1:1 ⁴. Darkroom folklore talks about XTOL dying without warning; Kodak's sheet, for its part, warns that partially filled containers let the solution oxidise ³.

The concentrates: HC-110, Rodinal, DD-X

The HC-110 of Kodak's J-24 sheet is a thick syrup, and the sheet is explicit that it is easier to make a stock solution first because of the viscosity ²; the formulation has changed over the years, so follow the instructions on your bottle. Straight from the concentrate the standard dilutions are A at 1:15, B at 1:31, E at 1:47 and F at 1:79 ². Here is a detail the forums love: Kodak's own table gives Tri-X 400 only 3¾ minutes in dilution B at 20 °C, on the same page that warns development times shorter than 5 minutes may give unsatisfactory results ⁴. That is the reason for the unofficial "dilution H", half the strength of B (1:63), which gives a longer time. It is not on Kodak's sheet and there is no fixed conversion, so test it before you trust a roll to it.

Rodinal is a para-aminophenol concentrate with a reputation for sharp, grainy, long-scale negatives. Ilford lists it for HP5 Plus at 1+25 for 6 minutes and 1+50 for 11 minutes at 20 °C ⁵; the high-dilution stand development people talk about is a community practice; Ilford's table carries no such time ⁵, so it belongs in your notebook, not here.

DD-X is Ilford's liquid for speed: it heads their list for HP5 Plus pushed to EI 1600 and 3200, at 1+4 for 13 and 20 minutes respectively ⁵, and it is the first developer Ilford names for Delta 3200, a film whose measured ISO speed is 1000 in ID-11 ⁶.

Specialists: fine grain, speed, stain

Ilford's HP5 Plus sheet is a little guide on its own. For the finest grain it names Perceptol, at the cost of speed (EI 200); for maximum sharpness, ID-11 at 1+3 or Ilfosol 3 at 1+9; for speed, DD-X or Microphen ⁵. Ilford's own pairing states the trade: Perceptol's finer grain comes with a lower EI ⁵, and the dilute options are the ones it names for sharpness. It is a tendency, not a law; Kodak describes D-76, a solvent developer, as giving full emulsion speed ¹.

Then there are the staining developers. Sandy King, in a long article at Unblinking Eye, explains that pyro and pyrocatechin developers leave a coloured stain in proportion to the silver, and that the stain adds printing density in proportion to the silver, so most in the highlights; his article goes into how that changes the way a negative prints, and why a stained negative reads differently when measured in visual or ultraviolet light ⁷. His Pyrocat-HD pairs pyrocatechin with a small amount of phenidone, which he describes as strongly superadditive with it ⁷. Pyro and pyrocatechin are toxic and absorbed through the skin; read the whole article, and use nitrile gloves, eye protection and ventilation whenever you mix or pour them.

Coffee

Caffenol is washing soda, vitamin C and instant coffee. Dirk Essl's caffenol.org quotes the Caffenol-C-M recipe as 54 g of washing soda, 16 g of vitamin C and 40 g of instant coffee per litre, 15 minutes as a starting point, for films up to 100 ASA ⁸, and publishes his own Delta-STD at 24 g washing soda (65 g if your soda is the crystalline kind), 20 g vitamin C and 45 g coffee per litre ⁹. Which washing soda matters: the recipes mean anhydrous sodium carbonate, and caffenol.org says to multiply the weight by 2.7 if yours is the decahydrate, the crystalline kind sold in some countries ⁹, so check the package for which it is; the vitamin C is ascorbic acid, and the recipes allow tablets ⁹. It works, it smells, and it is a fine way to find out how much of a developer is just alkali and a reducing agent.

One bottle

CineStill's Df96 develops and fixes in a single solution: 3 minutes at 27 °C with constant agitation, 4 at 24 °C with intermittent agitation, 6 at 21 °C with minimal agitation, each a minimum, with a tolerance of about one degree ¹⁰. The sheet notes that tabular films such as T-Max and Delta need double the time, to clear the pink and purple dyes in their emulsions, and that within its stated range pushing or pulling is done with temperature, 6 °C per stop ¹⁰. Less control, less to go wrong.

Safety

Every developer is an alkaline solution of reducing agents, and a used monobath also carries fixer and dissolved silver. Nitrile gloves, eye protection and ventilation when mixing and pouring; no powder in the air; and spent fixer and monobath kept for collection under local rules rather than drained.

Which one, then

If you are starting: ID-11 or D-76 at 1+1, one-shot, with Ilford's or Kodak's time for your film. You will get negatives that print and scan easily and a baseline to compare everything else against. Change one thing at a time, keep notes, and read the stop, fix and wash guide before you blame the developer for marks that were made later.