U of S | Mailing List Archive | alt-photo-process-l | RE: haunted GUM (related to judy's favourite pet peeve: the pigmentrat

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...)



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:

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)