U of S | Mailing List Archive | alt-photo-process-l | Re: gum preservatves

Re: gum preservatves

I am absolutely NOT going to test this myself, but one thought does occur to me reading Christina's very interesting excerpt from Demachy: As far as I know, Demachy and co ALL used a starch size (usually boiled, IIRC)... and as far as I know most of today's gum printers use a gelatin size. I DO know from personal experience that many variations in gum process play out very differently on starch than they do on gelatin -- so some of the following might also...

As I say, a thought....


On Thu, 4 Sep 2008, zphoto@montana.net wrote:

Demachy says:  “A strong proportion of citric acid or
a smaller proportion of more active acid added to the
mixture of gum and bichromate will utterly destroy its
sensitive properties; that is, will render it insoluble
without exposure to light to such an extent that repeated
friction with a sponge and hot water will scarcely affect
it.  We may, therefore, take advantage of this property to
counteract the excessive solubility of freshly prepared
paper and lessen exposure, giving more stability to the
half-tones.  A small quantity of a weak (say 5%) solution of
citric acid, or simply a few drops of lemon juice added to
the sensitive mixture, will start insolubilization and allow
of slower and surer development.  It is better, however, to
master the ordinary process before resorting to this
expedient.”  39

Have at it, Loris.  I found that the more lemon juice drops
I added to the mix (with drops of water added to the control
group in the same proportion) that I got lots of staining of
the highlights and lower contrast, but with paper negs this
might be helpful to you--I mean, the lower contrast part.
Step wedge steps were not too differentiated.