U of S | Mailing List Archive | alt-photo-process-l | Gum calibration (was: Paper negatives- Ink Selection)

Gum calibration (was: Paper negatives- Ink Selection)

Hi Keith,

What printer / ink and paper profile settings are you using? If you're
using grayscale negatives (which in your case could be giving more than
enough density range for gum), then you may switch to colorized ones which
are calibrated to give just enough DR!? (If that's the actual reason of
your relatively longer exposure times, of course...)

If I remember correctly, you weren't using curves, right? You have someone
very very competent in making digital negatives, who's living very close
to you ;) Why not asking them? (If you haven't already + If the current
exposure time is unbearable to you and/or you feel that you need to make
some improvements... Not to my eyes though!)

Maybe you can calibrate for a pre-determinated printing time (which you
find is bearable) such as say... 7:30 (1 stop faster) for your case, which
gives you a strong enough gum layer (has to be tested of course), then
fiddle with your working parameters (coating solution, curve, development
ect. ect.) to suit that printing time. It's right the opposite of the
usual (which is to determine the standard printing time for "a particular
coating solution + particular working parameters" with step tablet tests,
then design the curve based on that). I find the usual approach equally
awkward compared to what I just suggested -> with gum it's hard to be such
consistent, to test every possible coating solution, and why in world
would I want to leave aside all that flexibility provided by the process?

Any thoughts? (Especially to Mark, Michael, Christina...)

BTW, as a last note: if Keith's slow coating solution speed is due to low
humidity in his working environment, can adding glycerin (or propylene
glycol) to the coating solution (which are humectants) help to keep
moisture? Are dichromates and glycerin (or propylene glycol) compatible?
If not, then these additives could also help to thin the emulsion a little
bit (for better spreading), not to the extent water does. Plus, as an
added bonus,  since they're part of personal lubricants (I imagine Mark
making funny jokes here), I think they may also help in case of grabby
paper like Masa? :))


15 Ekim 2008, Çarşamba, 6:43 pm tarihinde, Keith Gerling yazmış:
> Hi Loris,
> My gums require 15 minutes with oiled negatives.  I would really like
> to reduce this.  Also, cyanotypes made with the same oiled negatives
> require exposure times of 30-45 minutes.  How does this compare with
> others?  It seems pretty long.
> Keith