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→Overview of the Process
After exposure, the plate is left to sit in the dark for a few minutes before processing begins. Fixing is first, and this can be done either chemically with a standard photographic fixer or optically with a few seconds exposure under intense white light. Washing is next to remove the dichromate from the gelatin. Finally comes the drying step, and this involves a sequence of progressively more concentrated isopropyl alcohol baths, the last bath being 99% alcohol. Hot air drying is next to remove the alcohol.
Once completely dry, the DCG hologram can be quite spectacular. The diffraction efficiency can be over 90% with no noticeable grain, and the hologram itself is very bright. Unfortunately, it will not last if the hologram is not sealed. Gelatin is hydroscopic, and therefore absorbs water. As water returns to the gelatin matrix, the hologram disappears. A common method to seal the hologram is to epoxy a second glass plate to the back of the hologram plate, thereby protecting it from moisture.
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