What Is in a Developer
A Developer formula balances four components:
| Component | Typical chemical | Job |
|---|---|---|
| Developing agent | Metol, hydroquinone | Reduces exposed silver halide to silver |
| Preservative | Sodium sulfite | Protects solution from oxidation by air |
| Accelerator or alkali | Sodium carbonate, borax | Raises pH to activate the agent |
| Restrainer | Potassium bromide | Suppresses fog on unexposed grains |
Classic formulas use superadditivity, pairing two agents that work faster together. Kodak D-76 is the industry standard metol-hydroquinone formula. Agfa Rodinal is a single-agent formula used at high dilutions for high acutance.
Dilution
The notation 1+31 means 1 part concentrate to 31 parts water. The working mix has thirty-two parts in total. To make 640 ml, divide 640 by 32. You use 20 ml concentrate and 620 ml water.
Time, Temperature, and Agitation
The standard processing temperature is 20 degrees Celsius. Development times change with temperature:
| Temperature | Multiplier on the 20-degree time |
|---|---|
| 18 °C | 1.20 |
| 20 °C | 1.00 |
| 22 °C | 0.85 |
| 24 °C | 0.72 |
Agitation brings fresh chemistry to the emulsion. Invert for the first 10 seconds, then invert for 10 seconds every minute.
The Sequence
- Stop bath: halts development instantly by lowering pH.
- Fixer: removes unexposed silver halides to clear the negative.
- Wash and dry.
Common pitfall: ignoring temperature drift. A shift of just 4 degrees Celsius alters development time by nearly thirty per cent. Always monitor temperature continuously.