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Type A - Acid process used in production of product. Primarily pork skins.

Type B - Alkaline process used in production of product. Primarily cattle hides.

Type B (bovine) - Alkaline process used in production of product. Specifically cattle bone. According to one supplier, this type may contain small amounts of silver salts which could increase speed of Silver Halide films although it was unknown how much (if any) effect this might have.

Bloom Stength - This is a standard measurement that determines hardness of gelatin after a specific period of time. The higher the Bloom number the harder the gelatin.

For Dichromated Gelatin emulsions, High bloom and type B is best.


  • It is best to gradually add the gelatin to room temperature water, let it swell up, then heat the swelled mixture while stirring to dissolve.
  • Cooking with too high a temperature destroys the gelatin - use a double boiler and thermometer or similar arrangemnet.
  • Knox Unflavored Gelatin has been shown to work well for DCG Holography.
  • Gelatin solution can be stored in a refrigerator and repeatedly reheated and reused for a while, but eventually goes bad due to mold etc.
  • Increase concentration of gelatin in water for thicker emulsion.
  • Heat glass to be coated for thinner emulsion.
  • Lower temperature of emulsion during coating for thicker emulsion.

Measuring the Hardness of Gelatin

It is possible to measure the hardness of gelatin according to an article by Oliva, Boj and Pardo (1983)

  1. Weigh gelatin.
  2. Soak the gelatin in distilled water at 18C of 15 minutes.
  3. Weigh gelatin again.
  4. The swelling factor is S=(W-W0)/W0%.

Higher values of S denote softer gelatin. For reference use:

  • AGFA 8E75HD plates had a swelling factor of 25. (Very hard)
  • Kodak 649F plates had a swelling factor of 200.

According to the authors of the article, this was why the Kodak plates were so much better for adaptation to DCG.