pre-fix wash?

Dichromated Gelatin.
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Joined: Thu Apr 30, 2020 9:46 pm

pre-fix wash?

Post by tommyNaN » Mon May 25, 2020 9:53 pm

See thread "DCG processing, comparing apples with oranges." Paraphrasing
Jeff Blyth and JohnFP, The important bit is that CR+3 is a hardener.

I was using K metabisulfite to kill off the CR+6, and reusing the solution,
since it was still working. However it was also becoming a more and more
concentrated hardener. So my holograms kept getting dimmer, and conflating
what I thought I was varying.

So the new hypothesis is wash out the CR+6 in distilled water. Which will
allegedly not wash out CR+5 and CR+3 in the exposed areas. Then fix with
K metabisulfite, which will turn all the CR+5 into CR+3, and cross-link, like
a hyper-active dark reaction. But it will not touch the unexposed areas
because the CR+6 which was there got washed out.

Does this seem plausable?


This hologram is:
18% 250 bloom gelatin, coated with a meyer bar
dried a week ago
sensitized in 5% K dichromate for 1 minute
quickly rinsed off in 1/2 % K dichromate, to avoid crystallization
dried overnight (about 12 hours)
exposed for 200 seconds at 100 uW/cm^2 457 nm
1 minute wash in distilled water
1 minute in 1 percent K metabisulfite
5 minutes in swelling bath at 24C
2 minutes in 70% at 24C
2 minutes in 91% at about 28C
2 minutes in 99% at about 28C
dried with a heat gun

The result was milky extremely wide-band, possibly widest I've ever made, with
very cool water. My previous attempts which looked like that were more like 34C.
Though also with 1/10 the dichromate.

I'm doing extremely long baths in the IPA to avoid chirping by giving it lots
of time to diffuse through the gelatin. It isn't working or I'm missing
something else, my results are very wide-band. What is the actual drying
mechanism? I thought it was diffusion/osmosis where the high concentration
water is encouraged to go to the low concentration water in the IPA.

The dichromate concentration is probably too high, others seem to use more like
0.5 percent, but my previous attempts were very dim, making me want to increase
it. (but they may have been dim because they were over hardened...)
The plate absorbed about 75% of the light (reducing 108 uJ/cm^2 to 27 uJ/cm^2),
measured with a power meter, plate held about perpendicular to the light. That
there is am image at all seems to support it being not completely wrong.

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Re: pre-fix wash?

Post by dannybee » Tue May 26, 2020 11:58 am

just looking at it, its need more hardness, the coin is nice but remember its close to the plate so its getting more light, where the other is back aways need more light or more hardening, usually when you do your hardening bath a lot of blue precipitating to the bath that's the way i tell its a good exposer and lot of crosslinking

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Joined: Thu Apr 30, 2020 9:46 pm

Re: pre-fix wash?

Post by tommyNaN » Thu Jun 04, 2020 6:56 pm

Yes, definately more hardener... but its weirder than that.

This one was sensitized with a 5% solution of K dichromate. If I do the same thing, only sensitize with a 3% solution, then its much more narrow band. In both cases, I washed it 1 minute in distilled water before the K metabisulfate. So there was very little blue in the K metabisulfate, but plenty of orange in the distilled water. It would make more sense if it was the other way around, harder in the 5% (because there was more K dichromate to harden the gel) and softer in the 3%.

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Re: pre-fix wash?

Post by PRATHEEP » Thu Oct 01, 2020 1:40 am

how can we maintain 50 degree temperature in dedicator?
during the dcg process meta bi sulfate best or thio sulfate best?

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Joined: Thu Apr 30, 2020 9:46 pm

Re: pre-fix wash?

Post by tommyNaN » Sun Oct 18, 2020 8:26 pm

My understanding is that sodium or ammonium thiosulfate is only relevent to silver halide chemistry. That the point to using photographic fixer is that it also includes a hardener. But my efforts did not get good results when I added a hardener (potassium alum). I used 1% potassium metabisulfate (and don't reuse it, the +4 chromium in it excessively hardens the next plate).

For dessicating the holograms at 50C, use a modified toaster oven with a PID controller thermostat off ebay?

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