RE: haunted GUM (related to judy's favourite pet peeve: the pigmentratio test)
Phritz, what happened with the desk lamp could be that you baked the emulsion under the (presumably) hot lightsource. How is the environment in your working area, and does it remain the same between tests? Humidity and temperature will affect your printing times (and fogging treshold) considerably. How do you coat and dry the prints. Do you rehumidity? Please tell us more about your procedures and environment... BTW I'm not familiar with poweder pigments (in the context of gum printing), but 0.5 - 1.2 g black powder pigment per 10ml coating solution looks like too much to me. FWIW, I use a very small (lentil or half lentil sized - haven't weighted, it but I'd bet it is below 0.1g) amnt. of powdered graphite per layer of casein dichromate to get a very satisfactory middletone density. (Graphite and carbon black are comparable, graphite being slightly less dense...) Regards, Loris. ________________________________ From: phritz phantom [mailto:phritz-phantom@web.de] Sent: Tuesday, October 06, 2009 2:29 AM To: alt-photo-process-l@usask.ca Subject: haunted GUM (related to judy's favourite pet peeve: the pigment ratio test) ... it was time to search for errors. i coated a sheet with 1,2gr of iron oxide black (not my favourite pigment), again with 5ml gum + 5ml pot-di, ripped it in three parts and made a comparison of the two different sheets of glass i use as printing frames and put the third one for 10min under the desk lamp that i often use during registration and such. the first two printed fine and pretty much the same. but with the third one, i noticed something strange. not only that there seems to be some uv present in the light of the desk lamp, but also: i left part of the sheet covered and it received zero exposure. and this part stayed completely black, not a whiff of pigment came off in the appr. 20min of development. here's a scan of the test strip: http://i31.photobucket.com/albums/c367/phritz/teststrip.jpg the part on top with the white stripe received ZERO exposure. i scratched off a little bit to show that the pigment is wet and soaked. it can be removed, it just doesn't want to come off on its own (nor did i have any success with brushing or sprinkling of water, only nothing or everything comes off) ...
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