Ewesly / Holographic Formulae / GP-2
0.2 g Phenidone
5 g Hydroquinone
100 g Sodium Sulfite (Anhydrous)
5 g Potassium Hydroxide
12 g Ammonium Thiocyanate
One litre water
Dilution: Add 15 mL of the stock solution to 400 mL of water before use.
Reflection holograms: twelve to fifteen minutes for plates.
Temperature: 20C Agitation: None
for developing Slavich PFG-03M plates. Doesn’t seem to work on the typical holographic stock like Agfa, Ilford, Harman, Fuji, Kodak. (Try it yourself and waste a plate if you don’t believe me!)
Not only does the development time seem out of step with the rest of the holographic processing world, which usually takes a few minutes, but the lack of agitation definitely sets it apart from the rest. This bath is a colloidal developer, and the silver that is reduced is not of the black filamentary variety, but very small spheres that appear golden-brown-orange, known as colloidal silver.
The Ammonium Thiocyanate acts as a fixing agent and dissolves the unexposed silver grains, which swim over to the developing grains in the bright fringes. It is sort of the same idea with a develop-rehalogenate processing scheme, with material moving from dim fringe areas to bright fringe areas, except in a single step developer that leaves behind tiny developed grains. Since there is no removal of material during processing, the replay color is the same as the recording. This processing is usually preceded by a formaldehyde hardening bath, and followed by a non-hardening fixer to avoid shrinkage.
Shelf life: The Stock Solution can last for months; discard when it turns yellow. The Diluted Solution lasts about a day in a tray.
Notes and References
Contrary to what Photographers' Formulary states, this formula was known for many years before any Soviet bloc holographic materials came on the Western market. Whoever invented this recipe is unknown to me at the moment, but since it’s such a low number, it might be fun to fantasize that it is one of the recipes used by Denisyuk at the dawn of reflection holography on one of Protas’s emulsions!