"dry" methods of increasing sensitivity without more exposure

Dichromated Gelatin.
Joe Farina
Posts: 814
Joined: Wed Jan 07, 2015 2:10 pm

"dry" methods of increasing sensitivity without more exposure

Post by Joe Farina »

From prior discussions on the forum, I've gathered that increasing exposure is not the best way to produce better DCG holograms. Besides increased risk of object movement, laser instability, etc., there are other factors.

One thing which Din had pointed out was that DCG does not have an exposure threshold, compared to silver (something I didn't realize) so that any stray light will cause noise. This would seem to be exacerbated by longer exposures.

Another factor is that DCG is a weak real-time material (according to what I've read). As soon as the exposure starts, a weak volume grating is being formed, which it seems would cause noise, again exacerbated by long exposures.

Years ago, I found that simple low-temperature heating was very helpful in my (rather complicated) color DCG tests. This was a long bake at ~65C/150F for 2 hours, post-exposure. One big benefit of this (which, I guess, could be called an accelerated dark reaction) is that it doesn't involve liquids, which can disturb the delicate fringe structure, especially if the liquids contain water.

Among the contributions which Jeff Blyth (and others) made to the forum, were discussions regarding the reduction of dichromate from Cr6 down to Cr5 and finally to Cr3. It seems to me that the more I can rely on the exposure to get to Cr5, and the less reliance in getting it all the way to Cr3, the better. The heating appears to have a good post-exposure reducing effect (Cr5 to Cr3). Traditionally, fixer/hardener has been used for post-exposure reduction (I substitute a water solution of sodium metabisulfite and aluminum sulfate). Although effective, this fixer step involves water, which I've become somewhat wary of when doing color DCG, which is more demanding than regular DCG.

Anyway, I've attached a photo of my outdoor DCG oven. The fumes are really bad, so I do this outdoors. The base for the oven is made from ceramic backer-board placed on concrete blocks, and the plywood box cover keeps the rain out.
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P1010046.JPG (68.74 KiB) Viewed 23527 times