Re: gum preservatves
Thanks Christina. Faster gum may mean a lot for some. For instance, I just finished calibrating for paper negatives and (for my light source + coating solution) the standard printing time is 15 minutes! I can surely use 1 stop faster gum... :) May suggestion wasn't waiting until it stinks. Maybe one can mix a small amnt. (such as 10ml) and note when it starts to stink. If that's - let's say - 3 days later, maybe one can wait 2 or 2.5 days and then add the preservative, just before it goes truly bad. I don't have a pH meter, if I had one I would certainly check pH change with time and see if I can get a more acidic gum that way... BTW, the curve I designed for 80 gsm photocopier paper negatives is the mildest I did until now! See it here: http://www.loris.medici.name/gum/Curve_Image.jpg (Curve applied to the negative image.) Negative info: HP9180, No Color Management, Grayscale, Plain Paper, Best. Coating solution info: Lightly pigmented (Schmincke Horadam 785 Natural Gray), 1 part 1:2 gum:water and pigment + 1 part 20% ammonium dichromate. Light source: 8x40W UVBL bank. Exposure time: 15 minutes. Tonal gradation is pretty nice but the print can't be considered smooth since the paper negatives fibrous structure shows in the print. No good for small prints but OK for big ones (which I currently intend to do)... Regards, Loris. 4 Eylül 2008, Perşembe, 4:52 pm tarihinde, Christina Z. Anderson yazmış: > > I'll chime in, Loris. Yes you are correct, but more acid also can lead to > more staining, and the smell of the gum is SO bad I would much rather have > a > 5 minute exposure and no smell than a 3 minute exposure and have to throw > up > every time I gum print :) > > I had made a huge batch of gum AND mixed pigment up into stock quantities > with unpreserved gum and had to throw the entire lot out. I suppose if I > didn't have a sensitive nose this would be no problem but I honestly don't > know how they did it way back when. > Chris > > >
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