Crystal structures forming after development

Dichromated Gelatin.
gorsholoforum

Crystal structures forming after development

Post by gorsholoforum »

Lately I have been having a previously unseen in my experience effect in which my plates form, what seems to me, crystal like structures in the plates in both exposed and unexpired areas. I have not changes anything significant in my process. I have tried a few different gelatin types (A, B with bloom strengths between 250 and 300) all of which were a subject to such crystallization. Had anyone faced such issue and found reasonable cause and solution?
Joe Farina
Posts: 804
Joined: Wed Jan 07, 2015 2:10 pm

Crystal structures forming after development

Post by Joe Farina »

Yes, I see those crystal structures very frequently with MBDCG. I call them "branches" and they are not welcome. They look like translucent white tree branches which quickly grow (within about 10 seconds), usually in the final 100% IPA bath. I was just discussing this problem with Martin, and he has seen the crystal structures in other types of DCG-type processes also.

The strange thing is, I didn't see them in regular blue exposed DCG (457nm with 200mW). This may be due to the fact that "normal" DCG typically involves a higher level of direct photo-induced crosslinking (hardening) as opposed to MBDCG. Probably a more important factor is that regular DCG has a higher level of hardness generally, due to the dark reaction which I've found to be useful in adjusting the bias hardness prior to exposure. These branches are very common in MBDCG, which doesn't seem to have much of a dark reaction (Jeff's formula), and the layer generally seems quite soft, unless special hardening steps are taken.

I think the main factor causing them is soft gelatin. The softer the gelatin is before processing, the more likely they will show up. They are obviously larger and more pronounced in the unexposed areas. Milkyness (an overall white translucent look without branches) is also due to soft gelatin. The crystalline structures (branches) may simply be a more extreme manifestation of "milkyness." I don't like it when the branches show up, because even when they become clear in the subsequent heating/drying step, they seem to contribute to noise. In the final heating/drying stage (60 to 100C), the branches often become whiter and more pronounced at first, but then later on, they often clear. I'm currently working on possible ways to reduce branching by hardening the layer at various steps in the processing.

I have no explanation as to what the branches really are, but I'm pretty sure they're related to the hardness of the gelatin in the processing stage when it contacts IPA in the 90 to 100% range. The fact that the layer will have previously contacted water (before the 90 to 100 IPA) may be significant.
gorsholoforum

Crystal structures forming after development

Post by gorsholoforum »

Thanks for the reply, at least now I don't feel alone in the universe. I'll be working on trying to figure this out. I'll post when I come up with a way too minimize this effect of wherever it is that causes it.
Kiffdino

Crystal structures forming after development

Post by Kiffdino »

we observed these "branches" aswell. They disappear if you dry long enough with the heatgun. The hologram will appear.
The result won't be great though.
250-300 bloom is very hard. I would look for a gelatin at 220 or even softer.
Joe Farina
Posts: 804
Joined: Wed Jan 07, 2015 2:10 pm

Crystal structures forming after development

Post by Joe Farina »

Kiffdino, congratulations on your work in DCG. It's very nice to see a group of young people working diligently with DCG in a suitable facility.

I really like this one:

https://www.youtube.com/watch?v=PIwWQMK ... r_embedded
Kiffdino

Crystal structures forming after development

Post by Kiffdino »

Thank you Joe. Those coins were the first nice hologram in our lab. Its then that we realized our gelatin was so hard 220 bloom that we get our best results when we shoot our plates immediately after coating.
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