D-25
An ultra-fine-grain metol-bisulfite developer for gentle development of old and expired film.
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.
Pros
- One of the most granular solutions on Metol
- Very gentle on old or expired emulsion
- Up to 7 films per liter of solution
Cons
- Long development time (30–35 minutes at 20°C)
- Partially used solution should be stored for no longer than 3 weeks
- Elevated temperatures (25°C) are not suitable for expired materials
Recipe for 1 liter
Chemical structures: PubChem (public domain)
Mixing it at home
A metol–bisulfite developer supplied in two packets. It works at a near-neutral reaction — hence its soft, gentle action.
- 1Pour 400–450 ml of distilled water at 40–45°C into a container marked at 1 liter.
- 2Dissolve the contents of the large package (sodium sulfite and sodium/potassium metabisulfite) in it.
- 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.
- 4Combine the two solutions and let them cool to 20°C.
- 5Add distilled water until the level reaches the 1-liter mark.
- 6Let the solution settle for 2–3 hours; filter it if necessary.
Key points
- The near-neutral bath is gentle and well suited to old and expired film — at the cost of some speed.
- Develop for 30–35 minutes at 20°C or 15–20 minutes at 25°C (higher temperatures are not recommended for expired photographic materials).