> When I started gum printing fifteen years ago there was no modern book
> about alternative photo process and no reprints available in french. I have
> some difficulty with English, so I was looking about french historical
> books. I have examined coolection of books in Library and buy also
> historical books about the
> gum. I found in this literature five option and tested 3 of them;
>
> -using fresh mixed gum (described by Puyo, Maskell, Demachy) which work
> very fine with the disadvantage of short conservation.
>
> -using formaldehyde,(described by Emery) this substance is toxic, have
> cumulutive effect and seem be cancer-producing. I used this option many
> years ago , but have some difficulty to develop prints coated with gum
> oldest more that 6 / 9 months. I have not definitive explanation of this
When you say you couldn't develop prints coated with gum after 6 or 9
months, I take it you mean the gum was 6 to 9 months old, and had been
"preserved" with formaldehyde.
The other possibility that occurs to me is that you hardened an allover
coat of gum used as a size with formaldehyde, then kept the paper for 6 to 9
months before attempting to print on it.
My experience is that gum "preserved" with a *small* amount of
formaldehyde kept very well -- about 2 drops in 2 ounces. Mine works fine
after a year, tho it's true I haven't made a comparison test to see if it
changed.
On the other hand, paper sized with gelatine and hardened with
formaldehyde has in the past gone off after a year or so (no matter that
the books tell us it keeps indefinitely). That is, the paper stained, pigment
didn't clear -- probably due to progressive hardening effect of the
formaldehyde.
Now I'd recommend glyoxal for hardening *gelatine* (tho am also testing
some other options); it's certainly less toxic and virtually odorless to
use. Paper cleared better with it than with formaldehyde (fresh paper -- I
never tested older paper). Any ideas out there on glyoxal in gum arabic?
However, I should add that the working solution of glyoxal doesn't
keep like the working solution of formaldehyde (which worked indefinitely
-- you could keep a jug going forever by topping it off when it got low). I
mentioned this a few weeks ago and since then did the following --
Mixed one jar of Glyoxal with distilled water, another with tap water,
neither of them used. Left alone on shelf. Less than 3 weeks later the
tap water had a blobbing homuncule in it -- sort of like the Michelin
man only translucent -- filling the center of the jar.
The one made with distilled had only a very small cloudlet at the bottom,
suggesting, what? Impurities in the "distilled"?
Whatever, you can't keep the glyoxal and use it again with that fellow in
it, which is the only problem I've had with glyoxal. But what that would
mean for glyoxal in gum I have no idea.
> -using salicylic acid,(described by L.P.Clerc, H. Schneeberger)this method
> give me satisfaction and I keep this option.
Does the salicylic acid come in different strenths? Or do you buy it
"straight"?
Judy