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25) I then leave the plate under a cold air blower for 20 minutes to acclimatize with ambient humidity. It is then best to leave the plate in a cardboard dark box until the next day when you are making larger holograms because the gelatin surface is probably not going to be stable enough for longer exposure times of more than say 4 seconds. However you will probably want to at least make some necessary exposure tests on small plate pieces before that. I find it best to do initial tests on a glass top table with the spread laser beam coming up from underneath the table or any frame able to hold a horizontal glass sheet. Initially it is best just to make a photographic exposure test. With the beam shuttered I place a piece of my recording plate on top of some masked off area , such as the piece of negative with lettering on it in the image below hat had been put in the beam before it was shuttered. The laser exposure times need to be sufficient to give a development time of about half a minute or less at 22C (see below under “Development Time” discussion). The “photographed” unmasked off area should look quite dark whereas the masked off area should be no more than slightly dark, ( if it is nearly as dark as the unmasked area than that means that I have a fog problem either caused by stray light or chemistry in the gelatin).
→Anti-Printout chemicals
23) If I want to make bright green holograms from a red laser, then I must not use the ascorbate bath but instead I immerse the plate in a bath of 15% triethanolamine or ”TEA” for about a minute. (Treating with both ascorbate and TEA causes chemical fogging or darkening without light involvement).
24) I then carefully wipe the surface free of droplets using either a wiper-blade squeegee or doubly folded tissue over a ruler similar to that used for the earlier AgNO3 treatment, (but now I do not have to worry about any contamination from chloride ions).
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