FilmDevMate
1+50 means one part stock to fifty parts water. Fifty-one parts in total. For 500ml, divide 500 by 51: about 9.8ml of stock and 490.2ml of water. A three-number dilution such as 1+1+100 works the same way, with two concentrates instead of one.
The mistake worth knowing about is reading 1+50 as one part in fifty. That gives 10ml instead of 9.8ml, which is a developer about 2% stronger than the recipe intends. Small, but it is the wrong direction to be casual in, and it compounds at lower dilutions. At 1+9, one part in nine gives 55.6ml where one part in ten gives 50ml, a 10% difference.
A 9.8 ml B 490.2 ml
Some developers come as two concentrates that are combined at the moment of use, because mixed together they do not keep. Pyro developers are the common example, and their dilutions are written with three numbers: 1+1+100 is A 1, B 1, C 100, where C is the water.
The arithmetic is the same, you just add all three. 1+1+100 is 102 parts in total, so for 500ml that is A 4.9ml, B 4.9ml and C 490.2ml. Use the button above to add the third part.
Two things specific to these. Mix each concentrate into the water separately rather than combining A and B first, and mix them immediately before pouring, because the working solution has a short life once the two are together.
| Dilution | 300 ml | 500 ml | 650 ml | 1000 ml |
|---|---|---|---|---|
| 1+9 | 30.0 ml | 50.0 ml | 65.0 ml | 100.0 ml |
| 1+25 | 11.5 ml | 19.2 ml | 25.0 ml | 38.5 ml |
| 1+31 | 9.4 ml | 15.6 ml | 20.3 ml | 31.2 ml |
| 1+50 | 5.9 ml | 9.8 ml | 12.7 ml | 19.6 ml |
| 1+100 | 3.0 ml | 5.0 ml | 6.4 ml | 9.9 ml |
Figures are part A, the concentrate. The rest of the volume is B, the water.
Working volume is set by the tank, not by preference. A single 35mm reel typically needs about 300ml and a 120 reel about 500ml. If a high dilution leaves you with an implausibly small amount of stock, the answer is a larger volume, not less liquid.
Several one-shot developers specify a minimum quantity of stock per roll regardless of dilution, because below it there is not enough active chemistry to develop the film fully. If the calculation puts you under that minimum, increase the total volume. Adding extra stock instead changes the dilution, and therefore the development time.
