Re: Gelatine - Borax - Formaldehyde

Maybe until 1970 formaldehyde, sometimes mixed with chrome alum, was
used as a hardener but generally it was replaced with glut and other
hardeners. So I don't know of good modern examples to begin with...

But if you look at old literature, formaldehyde is generally used at a
rate of 1 to 1.5g per 100g of dry gelatin. Formaldehyde hardened
material is generally allowed to sit for two full weeks before
use. (Chrome alum is also used at 1 to 2g per 100g dry gelatin, and
similarly, two to three weeks are allowed before use.)

If more hardener is added, gelatin will harden sooner, but then
gelatin will overharden afterward, and the quality won't be stable
over time. Plus, excess aldehyde agent may evaporate, or stay in paper
and cause problems.

Loris's prototype formula uses 20g formaldehyde per 100g of dry
gelatin, and this is a lot of hardener. More than 90% of this amount
of hardener will be wasted in some form.

I'd cut this to 2g or less and allow plenty of time for hardening. In
order to buffer the pH to alkaline region to optimize hardening rate,
borax can be used as suggested. Also, besides borax, disodium
phosphate or triethanolamine may be used. TEA also works as a mild
plasticizer. (Ammonia, primary amines, etc. should be avoided because
they'll react with the hardener, by the same mechanism as gelatin
crosslinking!)

Gelatin solution's pH varies depending on the gelatin. So the amount
of borax can't be determined without experimenting with the particular
gelatin. However, 0.2 to 1% solution of borax is probably a good
starting point.

As you see here, glut will simplify life a lot. You could simply stir
in 0.5 to 1g of glut per 100g dry gelatin and coat. By the time the
paper is completely dry, the hardening is done. There's little excess
hardener to worry about.
Received on Sat Jan 21 18:40:24 2006