U of S | Mailing List Archive | alt-photo-process-l | Re: another 3 layer gum attempt

Re: another 3 layer gum attempt

Hi Joe / Paul,

I use negatives with a DR of log 1.5 for gum. (DR is absolute dmax - dmin
of negative in this context; nothing related to zones...) That is exactly
what I need for 2A+1B traditional cyanotype -> because I don't calibrate
for gum, I just use negatives calibrated for 2A+1B cyanotype when printing
gum. Works extremely well. (And is very practical to me since I often
combine gum and cyanotype so I don't have to print two separate negatives
for that purpose...) As a matter of fact I couldn't get satisfactory
shadow detail with lower DR negatives. (That is thin negatives, something
like log 0.9 - 1.0 as suggested by many others...) Anyway, that's me, my
incompetence(!) ;) -> see it for yourself.

Will let Christina write about it (since she has vast experience/knowledge
about calibrating diginegs for gum), but I should mention that "to me"
it's a tiring process which in the end you have to act within very
specific limits, taking out a lot of the flexibility gum printing


-----Original Message-----
From: Joseph Smigiel [mailto:jsmigiel@net-link.net]
Sent: Wednesday, July 22, 2009 3:14 PM
To: alt-photo-process-l@usask.ca
Subject: Re: another 3 layer gum attempt


If you were to consider how Arentz et al would describe the DR (as I
understand his description from 90% black to threshold light gray
inclusive, i.e., steps 3-5 as a gum emulsion might print with a maximum of
steps 1-6 distinct) the gum negative density range might only be (5-3) x
0.15 = 0.30 and that ain't much.  You really need a thin, flat negative
compared to other processes.

Christina Anderson has done some wonderful work in gum using Mark Nelson's
PDN system to calibrate everything in the digital environment.  Perhaps
she'll chime in here with some digineg advice.