U of S | Mailing List Archive | alt-photo-process-l | Re: Gum Preservatives

Re: Gum Preservatives



I use Sam Wang's recipe of 1 drop 100% thymol solution (10g thymol in 10ml methylated alcohol) per 5 oz of mixed up gum. Works great.

I also used sodium benzoate very successfully. 1/2 tsp per every 100g dry gum. No mold or souring for a long time.

Believe me, I know about souring. First time I ever mixed gum I didn't preserve it, and it smells so horrible it'd make me puke. Had to throw the entire batch of not only gum but my gum/pigment mixes, too. WOW. I could never understand how back in the day they would let it sour on purpose because it was faster.

However, with the last batch for some unknown reason I tried the "more is better" school--if one drop is fine, maybe 5 drops will be better. It is way overkill--my mold is killed and so is my nose :) I did that once with glutaraldehyde hardener, if 6ml per liter was OK what would 30ml do? Way overkill.

So thymol goes a long way. 10g is not expensive, either. And neither is methylated alcohol, tho couldn't one use isopropyl?

It is interesting that Michael asked about using glyoxal as a preservative, because I never heard of it being that, and also, it hardens gum. But for some unknown reason they did use formaldehyde as a preservative in gum back in the day. Seems so strange to me.
Chris
----- Original Message ----- From: "Loris Medici" <mail@loris.medici.name>
To: <alt-photo-process-l@usask.ca>
Sent: Tuesday, December 05, 2006 10:48 PM
Subject: RE: Gum Preservatives


I wouldn't too. I used thyme water (which contains considerable amnt. of
thymol) in my first batch (3ml into 300ml) and the gum solution went bad
in just 2 weeks (serious mold growth). I used food grade Sodium Benzoate
in the second batch (according to the following recipe:
http://www.usask.ca/lists/alt-photo-process/2005/apr05/0247.htm. Please
note that I mean 5g Sodium Benzoate per 200g Gum Arabic powder. My
gum:water weight ratio is 1:2 - 100g gum powder into 200g/200ml water -
that's quite different from Guido's recipe!), and it's fine after 2
weeks - it looks, smells and works (and it works well!) just as it was 2
weeks ago... (I'm currently printing on aluminum)

Hope this helps,
Loris.

-----Original Message-----
From: Katharine Thayer [mailto:kthayer@pacifier.com]
Sent: 06 Aralık 2006 Çarşamba 05:19
To: alt-photo-process-l@usask.ca
Subject: Re: Gum Preservatives

You could, but I wouldn't. What you need is a biocide, while glyoxal
functions as a crosslinking agent. If you used enough glyoxal to
crosslink the gum enough to discourage mold growth, I suspect it
would also render the gum insoluble (thus unusable). In my
experiments hardening gum for painting, I found that a drop of
glyoxal hardened 5 ml of gum to a crystalline state. In general, I'd
say you want the crosslinking of gum to occur in the exposure phase,
not before.
Katharine

On Dec 5, 2006, at 6:31 PM, Michael Koch-Schulte wrote:

Can I use a few drops of Glyoxal in gum arabic as a preservative?
I'm mixing
the gum from powder.
~m