---------- Forwarded message ----------
Date: Tue, 17 Jun 1997 22:41:12 -0400 (EDT)
From: Art Chakalis <achakali@freenet.columbus.oh.us>
To: Judy Seigel <jseigel@panix.com>
Cc: alt-photo-list <alt-photo-process-l@sask.usask.ca>
Subject: Re: Gum consistency and preservatives.
On Tue, 17 Jun 1997, Judy Seigel wrote:
>
>
> On Tue, 17 Jun 1997, Art Chakalis wrote:
> > I use thymol in place of mercuric chloride. However, if you mix your own
> > gum solution you also need to keep it heated for a period of time to
> > destroy any enzymes that are found naturally in gum. However, too
> > much heat will degrade the gum itself. I typically heat to 140 F for
> > about 1/2 hour to deactivate the enzymes.
>
> Art, I happened to be in TALAS today, which has conveniently moved next
> door to my storied gym, buying various goodies (including TA DA! the
> Dahlia mister!!!) and asked about heating the gum arabic. Experts there
> had never heard of it, nor have I come across a mention of same in 97
> years of the "literature" on gum printing. I was advised to ask you, sir,
> for your references!!!
>
> In any event, I'm curious what the enzymes are supposed to do or not do.
Judy, Remember that I work in the food industry . . . guess who uses the
majority of the gum arabic (you've got one guess). Generically I sourced
several food scientists. Specifically, look up the following books which
I believe will bear out similar concepts (the 1st book calls out oxidases
and peroxidases which I understand to be enzymes by current nomenclature).
Also, the heat treatment I give is less than you'll find in either
reference, food scientist's recommendation to keep the heat degradation
minimized for my photographic applications.
"The Water-Soluble Gums" by C.L. Mantell, Ph.D.
Reinhold Publishing, 1947 (this one pre-dates ISBN numbers)
"Handbook of water-soluble gums and resins" McGraw Hill, 1980
ISBN 0-07-015471-6
> I've also parted with money recently in exchange for 100 grams of thymol
> in crystal form. Can you tell me what % solution to mix and how much you
> add to the gum solution?
I use .25%, your 100 grams will last you quite a while. By the way, this
stuff isn't real friendly so wear a respirator while handling the powder.
AND . . . I think you'll find both books very informative as to why you
get the variability that you've observed. I'm not really certain what you
can do about it though. Oh one other thought, look up Gum in your NY phone
book, some of the larger importers are in your neck of the woods and may
be willing to give you some other recommended reading.
I hope this helps, Sincerely, Art
Art Chakalis
Columbus, Ohio, USA
PS - Dry gum arabic has little water activity, therefor bacteria has a
tough time living off of it. In solution that is a different situation
which is why the thymol is added, it prevents bacterial growth.