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, firstname.lastname@example.org 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. Chris