Gelatin size reheated

[Dwayne Martin]

Do any of you gum printers out there know if I can mix gelatin with glyoxal use what I need, then store the remainder and reheat it to size more paper later? Or does it need to be one shot. My experience is that it will re liquify at least once or twice but after that it gets sort of globby and won’t turn completely liquid. Will the size perform the same reheated or does it create some sort of problem?
I can’t seem to find mention of this in any threads so far…
Thanks

 

[tezzasmall]

For use of Liquid Emulsions, it is recommended only to take out the amount of the emulsion required at the time, as remelting it again and again is not good for it. As it's mostly gelatin, I can only presume that this would apply to your process as well, but I could be wrong...?

Terry S

 

[Vaughn]

Once the gelatin starts to cross-link (due to glyoxal), I would expect that over time, it will be less likely to re-melt completely. But my experience is with gelatin and dichromates.

Can you just keep the gelatin prepared and on hand, and add the glyoxal to the melted amount you will be needing?

 

[Dwayne Martin]

Once the gelatin starts to cross-link (due to glyoxal), I would expect that over time, it will be less likely to re-melt completely. But my experience is with gelatin and dichromates.

Can you just keep the gelatin prepared and on hand, and add the glyoxal to the melted amount you will be needing?

I’m sure I could do that, that’s a great idea thanks.

 

[Vaughn]

If you have a hard time keeping mold from forming in the gelatin in long-term storage (even the fridge won't help eventually), thymol will keep the mold away (active ingredient for Listerine).

May not be as big of a problem than with carbon printing -- we add sugar to the gelatin.

 

[Dwayne Martin]

If you have a hard time keeping mold from forming in the gelatin in long-term storage (even the fridge won't help eventually), thymol will keep the mold away (active ingredient for Listerine).

May not be as big of a problem than with carbon printing -- we add sugar to the gelatin.

I started the thread because I had a decent amount of gelatin already mixed with glyoxal. I mixed it about two weeks ago. I re heated it last evening. After that much time it took a lot of heat to get it to turn liquid again. I couldn’t hold the bottle it was so hot. Presumably the glyoxal had cross linked like you suggested. I sized about 4 sheets of paper with two coats. It seemed to work fine but I’m not sure if it will perform as well as if it were fresh.
Thanks for the tip on the listerine. When you premix gelatin do you simply scoop a bit out of the jar and heat that, or do you reheat the entire jar?
Thanks

 

[Vaughn]

No. I mix as much as I am going to use...generally 3 liters. Then I pour my carbon tissues.

I often let the gelatin sit in hot water for several hours (up to 12) to let it de-gas, so a little Thymol is added to keep the mold away. The tissue can take a couple days to dry, so needs the protection of the thymol.

Thymol is bought in powdered form and must be mixed in alcohol, as it will not dissolve in water.

 

[M Carter]

PE mentioned this in the emulsion forum here - "once you add the hardener, the clock is ticking". I consider glyoxal in gelatin to be one-shot, but I measure glyoxal in drops and just use an eye dropper. In my experience, it doesn't need to be insanely accurate measuring.

I've been spraying Foma liquid emulsion onto canvas, and I use the included hardener (I assume it's chrome alum?). It takes three or four coats to properly coat, and the emulsion has to dry pretty well between coats, so it's maybe 30-40 minutes overall; I find in that time period, the emulsion still sprays well if kept warm, the hardener isn't setting up yet. I do clean the gun between coats though. But I dispose of leftover emulsion when I'm done, hate to toss it but my assumption is it won't be workable days later.

 

[Andrew O'Neill]

I wouldn't bother storing mixed gelatin. It's too easy to mix up to begin with. I only mix what I need. 400ml will give me 5, 8x10 tissues for carbon transfer printing.

 

[Vaughn]

The supplied hardener for the Foma Liquid Emulsion might be Potassium alum -- slower acting than the Chrome alum...and has a low toxicity level. A guess since they do not disclose what it is. The instructions seem to suggest both fermaldhyde and Chrome alum as being alternatives to the supplied hardener, but are somewhat ambigulous.

From Foma's website:

Hardener to photographic emulsion:
We declare hereby that the supplied substance (mixture) does not meet the criteria for classification as dangerous according to Directive 67/548/EEC (or 1999/45/EC) or Regulation
1272/2008/EC.
Under Art. 31(1) of Regulation (EC) No. 1907/2006 of the European Parliament and of the Council, there is no obligation to compile a Safety Data

I would think Chromium in any form would warrant a mention.