DCG Recipes

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Rallison introduced a notation for basic recipes for dichromated gelatin emulsions. He use a sequence of three numbers that indicated the quantities of dichromate, gelatin, and water, respectively, used in the formulation. For example, 5-30-200 in Rallison's scheme meant 5 grams of dichromate with 30 grams of gelatin and 200 grams (exactly equivalent to ml) of water made up the recipe. The normal for Rallison's notation was 30 grams of gelatin, while the dichromate and water ratios were allowed to vary.

Many amateur holographers use common food-grade gelatin in their work. Knox Gelatin is the most typical. In the United States, Knox Gelatin is available in convenient ¼ oz. packets. An ounce is roughly 28.3 grams, so it can be useful to express Rallison recipes using a 7.1 gram (quarter ounce) reference for gelatin instead of the more common 30 grams. Common Rallison recipes then become:

Ralston Recipe Rescaled Recipe
5—30—250 1.2—7.1—59
10—30—600 2.4—7.1—142