Re: Copy of: buying Gum Arabic
Judy Seigel (jseigel@panix.com)
Thu, 30 May 1996 01:58:00 -0400 (EDT)
On Wed, 29 May 1996, Martin Becka wrote:
> > How much salicylic acid.
>
> L.P.Clerc in "La Technique Photographique"(1942) wrote
> Add 2 or 3 g salicylic acid to 1000 ml mixed gum
> ( 500 g gum add water to make 1000ml )
>
> H.Schneeberger in "Les procedes au charbon"(1937) wrote
> Add 5 g salicylic acid to 1000 ml mixed gum
>
> C.Puyo in "Le procede a la gomme bichromatee" (1904), and A.Maskell et
> R.Demachy in "Le procede a la gomme bichromatee" wrote that's better work
> with fresh mixed gum.
>
> I add to my home-mixed gum ( 500 g gum, water to make 1000ml ) 3 g
> salicylic acid.I print trichrome or polychrome gums and I have in my lab
> many bottles, some of them are 1 year old and I can work fine with them.
>
Martin, that's an impressive pharmacopeia. Perhaps you know if there's
some reason for using salicylic acid in preference to, say, formaldehyde,
glyoxal, or thymol, other than (presumed) lower level of toxicity?
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.
Judy