D-25

About the Developer

D-25 is characterized by its simple formula and excellent developing properties. Thanks to its virtually neutral reaction, this developer is very gentle on old photographic film emulsion—damage to the emulsion is virtually impossible as long as the temperature is maintained within the specified range. Metol acts very gently in this solution under neutral conditions: the development of each silver halide crystal, as soon as it begins, is slowed by a local decrease in the solution’s alkalinity, causing the silver grains to remain small. The large amount of substances that dissolve silver halide further prevents the grains from coalescing into large crystals.

Character

An ultra-fine-grain metol-bisulfite developer that operates at a nearly neutral pH—it has a gentle, non-aggressive effect on old emulsion, resulting in a slight loss of sensitivity.

Best films

The source does not provide specific data on particular films; according to the description, it is particularly effective for old and expired black-and-white film, where gentle, rather than aggressive, development is important.

How to Prepare and Use

1. 1Pour 400–450 ml of distilled water at 40–45°C into a container marked at 1 liter.
2. 2Dissolve the contents of the large package (sodium sulfite and sodium/potassium metabisulfite) in it.
3. 3In a separate container, dissolve the contents of the small packet (metol) in 300–350 ml of water at 40–45°C, carefully breaking up any lumps.
4. 4Combine the two solutions and let them cool to 20°C.
5. 5Add distilled water until the level reaches the 1-liter mark.
6. 6Let the solution settle for 2–3 hours; filter it if necessary.
7. 7Develop for 30–35 minutes at 20°C or 15–20 minutes at 25°C (higher temperatures are not recommended for expired photographic materials).