Re: Gum Arabic Powder lifespan

Bas van Velzen (eland@knoware.nl)
Wed, 17 Jul 1996 10:54:13 +0100

>I have access to a few pound containers of Gum Arabic Powder and
>Crystals. It's very inexpensive. I believe it's used in lithiography. My
>question is, should I be concearned about the quality?Could it be much
>different from say what I get from Photographic Formulary? How long will
>it last? And finally, Is the crystal or powder better for Gum Printing?
>
>
>Thanks again for your advice!!!
>
>Macy Garcia

When kept dry and in the dark, at reasonable low temperatures (
<20=B0C, in the tropics you will have problems) there should nothing be wron=
g
with the gum. Powdered gum is usually refined in some way so it will be
pretty clean. It can be kept for ages in this way. The difference between
crystals and powder is to my knowledge no big deal. Powder is made by
grinding, breaking, crystals are made by drying a gum solution in rotating
drums and the like. They only differ in size of the particles.
In my opinion dry gum has the advantage that when you make a
solution you can adjust its viscosity (do I hear a rumble in the
applebaume?) and you are shure there are no additions in the solution
(preservatives, colorants, lubricants etc.). So anything you put in it you
can control and there are no nasty surprises because there is something
unexpected in the gum.
Looking up gum arabic in the excellent book:

Materials for conservation
Horie C.V.
Butterworths 1987
ISBN 0 408 01531 4
pp 141

learns that it is a high molecular weight polysaccharide incorporating
calcium, magnesium and potassium. The molecules can be cross-linked and
precipitated by trivalent metal-ions, e.g. aluminium and iron salts, lead
and mercury salts and GELATINE!!!!

maybe this is a lead to further gumperience, who??

Bas

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