gelatin transparency

Dichromated Gelatin.
Joe Farina
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gelatin transparency

Post by Joe Farina »

Steven, you didn't mention your filtering method, but I've had good results with a syringe filter. I use a plastic syringe with a luer-lock end, a clamshell-type syringe filter (which has two pieces that screw together) and the replaceable filter-discs. The filers I use are 1.5 micron "glass microfiber" which are supposed to have a high flow rate. They have cheap, disposable syringe filters on eBay, but I prefer the clamshell type which are made by Whatman (may be rather expensive, though). The disc filters can be a bit difficult to locate, mine were bought from http://www.grainger.com They may have better/cheaper solutions on eBay, I haven't checked recently. 2 microns will probably work just as well, and may have better flow. I've had no problem with the 1.5 micron, but I do let the whole assembly warm up in warm water prior to filtering, this may be a necessity.

300 bloom type B gelatin is very hard (the limit, as far as I know). Might be worth a try.
dannybee
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gelatin transparency

Post by dannybee »

ther is a way to do dcgs in hard gel , it has a softer bath i will look for the pdf... it works well and can be used on any geltin plate or film :D
Joe Farina
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Joined: Wed Jan 07, 2015 2:10 pm

gelatin transparency

Post by Joe Farina »

To update the "transparency" issue, the gelatin has been melted and gelled, and a photo under yellow safelight is below. The photo doesn't show the relative transparency, because the lighting is uneven. But it seems tolerably clear that there's little difference in visual transparency among the 4 gelatin types. When the granules were saturated, but not melted, the 4 varieties looked quite a bit different.

The Knox may be a trifle darker, but not much. So I would be inclined to say, in this case, that the "transparency" of the gelatin itself is of little or no consequence.
Attachments
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Steven

gelatin transparency

Post by Steven »

Joe Farina wrote:Steven, you didn't mention your filtering method,
I do a single pass using ordinary lab filter paper and plastic funnel, using a hairdryer to warm the funnel before and during use.
I don't have any air filtering (HEPA) here, so a single pass to remove fine air bubbles and surface scum is fine.
A glass funnel would be better as it tends to hold the heat better, something else to buy.

I have used disposable syringes before for transferring the gelatin solution to the glass plate, but I have found that after a couple of uses the plunger starts to get a bit tight. I now filter into a plastic squeezy bottle and use that to apply the gelatin to the plate. I have had far fewer bubbles in my castings since using the latter method, a liberal supply of gelatin also helps:-)

Thanks for the info on syringe filters. I may need to try that method when I actually need to use the 300 bloom gelatin for MBDCG.

Steven.
Dinesh

gelatin transparency

Post by Dinesh »

Joe Farina wrote:yes, I was also wondering what Dinesh had in mind by "smoothness"
I mean that there must be no local density variations. It must be as homogenous as possible. If the local density varied by a few percent over even as small a distance as lambda/10 then it would form a scattering centre. A good demonstration of this is to fill a pint glass with water. Then shine a bright white light into it. Then add milk into it, drop by drop. Soon, a blue haze develops coming off the sides and the directly transmitted light begins to go reddish. This is due to the local density difference between milk and water. Sometimes micro-bubbles appear in the gelatin, for example, that aren't easily visible, but they form scattering centres which scatter blue to a much larger extent than any other wavelength. Sometimes you get crystal growth inside the gelatin once you add the dichromate and this too is a scattering centre.
Dinesh

gelatin transparency

Post by Dinesh »

dannybee wrote: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
Not sure how a coffee grinder will help. It may gum up your coffee grinder, but gelatin already comes as a pretty fine powder, finer than coffee granules out of a grinder.
Joe Farina
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Joined: Wed Jan 07, 2015 2:10 pm

gelatin transparency

Post by Joe Farina »

Dinesh wrote:
Joe Farina wrote:yes, I was also wondering what Dinesh had in mind by "smoothness"
I mean that there must be no local density variations. It must be as homogenous as possible. If the local density varied by a few percent over even as small a distance as lambda/10 then it would form a scattering centre. A good demonstration of this is to fill a pint glass with water. Then shine a bright white light into it. Then add milk into it, drop by drop. Soon, a blue haze develops coming off the sides and the directly transmitted light begins to go reddish. This is due to the local density difference between milk and water. Sometimes micro-bubbles appear in the gelatin, for example, that aren't easily visible, but they form scattering centres which scatter blue to a much larger extent than any other wavelength. Sometimes you get crystal growth inside the gelatin once you add the dichromate and this too is a scattering centre.
Thank you Dinesh, I printed a hard copy of your comments in this thread for my records ;)

At the moment, I'm using 532 and 633nm, but previously with 457nm, I did see some odd effects. In much of my reading, and in many of your posts, a rather abrupt transition is indicated, with regards to the importance of scattering effects, when blue is involved. A laser beam entering a cube of gelatin, with the scattering observed from the sides of the cube, seems like an excellent test for scattering, as you suggested. Those are interesting points about the micro-bubbles and crystal growth, thanks.
dannybee
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gelatin transparency

Post by dannybee »

well I'm going to try just of the heck of it, their are many degrees of fine ness in coffee gowns, my wife got me a hand grinder to make my coffee really fine I will report back in new thread :D
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