Kodak D-76 is a powder developer for black and white film in the large size: 3.78 litres (one US gallon) of working solution.
What it is for
The same classic formula as the one-litre sachet, four times the quantity and noticeably cheaper per litre. A universal developer that works well with any black and white film: a little more contrast and grain than the fine-grain formulas, in exchange for complete predictability and the most thoroughly published time table in existence — every film manufacturer prints one.
How to dilute it
The solution is replenishable — kept and reused, with development time extended as it exhausts. Keep count of the films put through it; that is the only way to avoid an underdeveloped roll at the end of its life.
Storage
Sealed powder keeps for years; mixed solution keeps far less well, so mix what you will use. Dissolve at the stated temperature and in the stated order — getting the order of components wrong ruins a developer more reliably than any timing mistake.
How it compares
The gallon size makes sense if you develop regularly and keep the solution in use. If you shoot a few films a season, take the litre — mixed D-76 does not keep forever.
