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Dichromated gelatin, or DCG, holograms are phenomenally bright. Unfortunately, gelatin is hygroscopic, meaning it has a tendancy to absorb water, and as the gelatin reabsorbs the water removed by the alcohol baths, the hologram will fade away. To preserve the hologram, it must be sealed from moisture, usually with some type of epoxy.
Dichromated gelatin is roughly 1,000 times less sensitive to light than the typical silver halide film, and even then it is most sensitive at the short end of the light spectrum (blues and violets), moderately sensitive to greens, and virtually blind to reds without some complicated chemical treatment to improve its red sensitivity. Most DCG holograms are produced using green or blue lasers at the higher end of the power scale, 100 mW or moreat 532 nm.
A serviceable 100 mW green laser suitable for holography may be out of reach of the hobbyist wanting to just give DCG a try. Nonetheless, modest sized holograms can be produced with modest power lasers. The image on the right shown here was created by a newcomer to DCG techniques, John Fisher. A handful of 1/4"-20 socket-head screws were the subject; the glass plates, 2 x 3" large microscope slides, and the laser used was a Coherent C215M-10 operating at a lowly 10 mW.
== Overview of the Process ==
