DK-20
An ultra-fine-grain metol-rodanide developer that reduces grain and light sensitivity to achieve maximum smoothness in the negative.
About the Developer
DK-20 is an ultra-fine-grain metol developer for photographic film, well-suited for processing light-sensitive photographic materials. Thanks to potassium thiocyanate (a silver solvent), it reduces grain size by approximately 25%, but reduces the film’s effective light sensitivity by about 30%.
Character
An ultra-fine-grain metol developer containing a silver solvent (potassium thiocyanate). It reduces the light sensitivity of photographic materials by approximately 30% and grain size by approximately 25%.
Best films
The source does not provide specific data on particular films; historically, it was intended for high-sensitivity roll film, where minimal grain is the most important factor, rather than maintaining full sensitivity.
Pros
- The finest grain size among methylol developers
- Potassium rhodanate, when used as a solvent for silver, further refines the grain
- It operates even at elevated temperatures (up to 32°C) with time compensation
Cons
- A noticeable loss of light sensitivity (~30%)
- Long development time (15–31 minutes)
- Limited shelf life—no more than 2 weeks
Recipe for 1 liter
Chemical structures: PubChem (public domain)
Mixing it at home
An extra-fine-grain metol developer with potassium thiocyanate, a silver solvent.
- 1Pour 500–600 ml of distilled water at 45–50°C into a container marked at 1 liter.
- 2Dissolve the contents of the first (large) bag—sodium sulfite, borax, potassium bromide, and potassium thiocyanate—in it until all the lumps have completely dissolved.
- 3In a separate container, dissolve 50–70 ml of the solution from the first container in 200–250 ml of water at 45–50°C, then add and dissolve the contents of the second (small) packet—metol.
- 4Immediately combine the two solutions and let them cool.
- 5At a temperature of 20°C, add distilled water until the level reaches the 1-liter mark.
- 6Let the solution settle for 2–3 hours, then filter it through cotton wool.
Key points
- The potassium thiocyanate etches the grain edges for very fine grain at the cost of some speed; an over-worked solution can produce dichroic fog.
- Develop with fresh solution for 15–25 minutes at 20°C (for some films, the time may range from 14 to 31 minutes).