Re: Copy of: buying Gum Arabic

Bas van Velzen (eland@knoware.nl)
Fri, 31 May 1996 12:02:27 +0100

>Does the "acid" have any effect on pH of the Gum? Perhaps not in those
>amounts, but what comes to mind is that apparently gelatine size needs
>some alkaline environment to prevent the hardener (formaldehyde, glyoxal)
>links from reversing, in which case the gelatine washes away. Of course
>maybe the other preservatives are equally acid .... but then again maybe
>they're not.

Salicylic acid (2-hydroxybenzoeacid) HOC6 H4 COOH

COOH
|
/\ OH
/ \/
| |
\ /
\/ this tries to be a representation of a phenolic ring
(think the "O" in the honeycomb yourself) with the COOH (acid)
group on 1 and OH on 2. pH saturated solution 2,5. Acid and
salts turn red in the presence of Fe(III). Sublimes at 76 C, light
sensitive. It is the base to synthesise aspirin, dyes and flavours.

Formaldehyde HCOH

H - C = O
|
H

pH 3-4, strong reductor specially in
alcaline solutions

to help in the confusion,

Bas van Velzen

Jonge Eland papierrestauratie
eland@knoware.nl
t +31 20 623 79 89
f +31 20 627 32 23

VeRes (Dutch Association of Professional Restorers)
postbus 11503
1001 GM Amsterdam

PAPER IS ART IS PAPER IS ART IS PAPER IS ART IS PAPER IS ART IS PAPER