gelatin transparency

Dichromated Gelatin.
Joe Farina
Posts: 804
Joined: Wed Jan 07, 2015 2:10 pm

gelatin transparency

Post by Joe Farina »

I was wondering if the transparency of the gelatin itself has an effect with 25-micron thick DCG. I am working on four batches which are shown in the photo. The gelatin has been stirred into the cold water, and the granules have not melted yet. From left to right: Knox, Great Lakes Type B, Photographer's Formulary (supposedly Kodak, type B?) and Great Lakes Type A. The photo doesn't show it clearly because the granules are not melted yet (and the lighting is uneven), but there is quite a variation in transparency, the Knox is quite dark, the Great Lakes B is lighter, and the other two are quite light, and look clearer. I will have a better idea of the transparency once they are melted. The bottles are about 2 inches in diameter.
Attachments
P4290036.JPG
P4290036.JPG (45.78 KiB) Viewed 3998 times
Joe Farina
Posts: 804
Joined: Wed Jan 07, 2015 2:10 pm

gelatin transparency

Post by Joe Farina »

I forgot to mention that Knox is supposed to be a mixed A + B gelatin. Cristiano Perrucci mentioned that he used such a mixed (A + B) gelatin for his stunning MBDCG hologram shown here:

http://www.youtube.com/watch?v=rfuel2NuruU
Steven

gelatin transparency

Post by Steven »

Hi Joe,

I ran out of my stock of gelatin a few months ago, so I ordered another bag of the same gelatin, from the same supplier.
Both were 240 Bloom. The second batch looks to be clearer, both in the dry state and when in water.
Apart from the colour, the only difference I can perceive between the two is that the second batch looks to be harder.

I'm using this stuff:
http://www.ebay.co.uk/itm/CLASSIKOOL-24 ... 485560ed89

Steven.
Tony DCG
Posts: 147
Joined: Thu Jan 08, 2015 1:47 pm

gelatin transparency

Post by Tony DCG »

I imagine it's all about wavelength absorption of light right?
If you ever want me to run some non-AmDi plates (or better yet a cubit of gelatin) into a spectrophotometer I’d be happy to help out Joe.

Good topic
Joe Farina
Posts: 804
Joined: Wed Jan 07, 2015 2:10 pm

gelatin transparency

Post by Joe Farina »

I saw a chart, it may have been from Gelita, with the transmission of light though different types of gelatin, both A and B. So far, I haven't been able to locate it again. Since I know these gelatins were for photographic use, I believe the figures were for thin films. The type A was shown to have quite a bit more transparency, perhaps something like 4% more (?) Since photo film is much thinner than what I'm using, I'm wondering if gelatin transparency can become an issue. Probably just taking measurements with 25-micron layers of the various types of gelatin, using a photo-detector, would be the thing to do.

Interesting, Steven, that you're using a type A gelatin.
Dinesh

gelatin transparency

Post by Dinesh »

Joe Farina wrote:I'm wondering if gelatin transparency can become an issue.
There are two issues here...no wait, there are three issues here....no wait, there are {The Spanish Inquisition has two weapons: fear and surprise. Our weapons are fear, surprise and ruthless efficiency...no wait, the Spanish Inquisition has three weapons.... )

Seriously, though, there are three effects: actinic reaction, absorption and scattering. The scattering issue is comprised of two types of scattering: Mie and Rayleigh. The light passing through the system of dichromate and gelatin can be considered independent, in that, the loss/unit distance of both the actinic reaction and the absorption of gelatin is just the sum of the individual losses I(x) = I(0) - I(actinic) - I(gelatin). The actinic part just concerns the laser wavelength. We can model this in terms of the activation energy of the cross linking process. Thus, if each cross linking event causes a loss of hf Joules, and the density of cross linking locations is N, then I(actinic) = hfNA/unit distnce, where A is the beam cross section area. The question then is: what is I(gelatin).

You have two processes occurring: scattering and absorption, So I(gelatin) = I(absorption) + I(scattering). The absorption will be lambda dependent, so a transmission plot in a spectrophotometer will give you the absorption loss. The absorption will probably depend on the constituents of the gelatin, since absorption implies absorption of a photon, then a change of energy in the molecule. This process depends on the molecular structure of the gelatin. You may be able to use the Kramer-Kronigs relations to model this, if you knew the gelatin density. I think the real problem is the scattering. If the molecule is large, there will be Mie scattering, but Mie scattering is essentially a white light phenomenon, and so is irrelevant in terms of recording. However, the Rayleigh scattering is proportional to the fourth power of the frequency, and you generally use high frequencies, optically speaking, to record a dcg hologram. Thus, the scattering is exacerbated by the fact that it's necessary to use blue-green to record. However, this also will depend on the gelatin density, but, in addition, it will depend on the smoothness of the gelatin, since the smoother the gelatin, the fewer the scattering centres. One way to test this would be to shine your recording wavelength into a cube of the gelatin and note the light coming off sideways.
Joe Farina
Posts: 804
Joined: Wed Jan 07, 2015 2:10 pm

gelatin transparency

Post by Joe Farina »

Thanks Dinesh. The point about the relevance of scattering is especially helpful. There are times when I've noticed a slight "turbidity" (for lack of a better word) with Knox gelatin. The photo-grade gelatins seem noticeably cleaner in this regard. Yet for some odd reason, I've had reliable results with Knox. Probably, I'm prejudiced because of this. It's not even known what the Knox contains, some have claimed it has a lot of extra material in addition to the gelatin. The Great Lakes gelatin, in the form I've received it, is also a culinary-type gelatin. For the Great Lakes, I will find out soon if the turbidity is comparable to Knox for the type B, but I have a feeling the type A will be clearer. The Photographic Formulary's gelatin is very clear.
Steven

gelatin transparency

Post by Steven »

Joe Farina wrote:Interesting, Steven, that you're using a type A gelatin.
I think pig skin gelatin is probably more readily available than bovine.
I just got lucky with my first choice of pig skin gelatin as it worked, so I have stayed with the same supplier.

I have got some bovine gelatin with a 300 bloom strength in the hope that I may give MBDCG a try in the future.
The bovine gelatin looks looks darker than the pig skin stuff and is almost impossible to filter as its sets a lot quicker, I tried it once. :(
I will need to work at a higher temperature when using the bovine gelatin.

From: http://holowiki.nss.rpi.edu/w/images/c/ ... l_2012.pdf

"The initial extraction usually provides a superior product, compared with subsequent extractions. Earlier extractions
have higher molecular weights, higher viscosity, higher gel strength, and lighter color. The
later extractions are made at increasingly higher temperatures; the resulting product has
lower molecular weight, lower gel strength, and darker color."

This would explain why my second batch of gelatin which is clearer than the first, is harder.
dannybee
Posts: 642
Joined: Tue Jan 06, 2015 10:29 pm
Location: visalia
Contact:

gelatin transparency

Post by dannybee »

so dinesh if its "smoothness of the gelatin' your looking for in dcg is ther ways you can process the gelatin or brake down its consistency? like run the dry gelatin threw a coffee grinder, just a idea :D
Joe Farina
Posts: 804
Joined: Wed Jan 07, 2015 2:10 pm

gelatin transparency

Post by Joe Farina »

dannybee wrote:"smoothness of the gelatin"
yes, I was also wondering what Dinesh had in mind by "smoothness"
Post Reply