Re: source for glutaraldehyde

On Mon, 06 Mar 2006 09:27:42 -0500 (EST), TERRYAKING@aol.com said:

> It would be interesting to know what is the the ' alternative' process
> in
> which hardener is so essential.

Silver gelatin process requires good hardener in both sizing and the
emulsion. If I use multilayer coating, or even plain gelatin overcoat,
the hardener is also very essential.

First of all, emulsion is coated hot. If the size isn't hardened, the
size will dissolve and the emulsion reaches to the paper. This is no
good.

My darkroom is air conditioned, but it is set at 25C during summer. At
this temperature, gelatin dissolves into processing solution and it's no
good.

Among emulsions I make, the best ones are made with very low viscosity
gelatin, well below 200 bloom. These gelatins are oxidized and acylated
to chemically modify the methionine and lysine in the gelatin. These
gelatins are essential in making good tabular emulsion in my hand.
Higher bloom gelatin is added later.

Incidentally, lime treated gelatins are extracted in a sequence. The
first extraction run always produces gelatin of higher molecular weight
and greater viscosity. The second extraction produces slightly lower
molecular weight, and so on. The later extractions are carried out at
higher temp. For better mechanical and rheological properties of gelatin
for sizing and overcoat, it's probably better to select gelatin from
among those with low extraction numbers.

Also, for non silver gelatin processes, don't dismiss acid treated
pigskin gelatins. As long as you can find a high quality gelatin with
good clarity and high molecular weight, they can provide better wet
strength than lime treated ossein gelatin commonly used in photography.
Food gelatins are generally very low viscosity, low molecular weight and
they are not the best choice but I've seen high quality pigskin gelatin.
(jellos made with high MW gelatin would be too tough in the mouth!)
Received on Mon Mar 6 14:09:08 2006