[alt-photo] Gum Printing: Looking for some wisdom

[Darkrooms, Department of Art]

Hello all,

I have been following this list serve for about two months now and what a
wealth of knowledge you all have!  I am hoping that you might give me some
words of guidance as I attempt to tackle gum printing.  Before I ask my
questions I would like to give a little background on how I will be using
this process and where I amŠ

I am the Photo Technician at Cornell University and we have been teaching
an alternative processes course using Litho and digital negatives.  This
past winter break I started using the quad tone rip and we are adding Gum
printing to the list of processes covered.  I have had fantastic results
creating negatives with Quad Tone RIP for Cyanotype, VanDyke Brown and NA2
Platinum.  I am just starting the process with Gum and having only dabbled
in gum briefly about 3 years ago I am getting a little tripped up with the
process.  

So far I have completed the dot test that is outlined in the Keeper of the
light to determine Pigment to Gum ratios for each color I would like to
use.  I have completed this on both the Fabrino Soft Press (un-sized) that
was discussed a few weeks back and Rives BFK sized in Gelatin and hardened
with Glyoxal.  The dot test looked great and I am now moving on to
determining a base time for printing with pictorico.  I am starting my
tests with Winsor Newton lamp black 1/2g in 60ml of gum arabic mixed 1:1
with  Potassium dichromate and another with Ammonium Dichromate.  I
completed a time test with a strip of pictorico using 4 minute increments
up to 32 minutes with each sensitizer on both Fabrino and Rives paper.  I
am using a homemade exposure unit that consists of a bank of closely
spaced black light UV florescent tubes approximately 3 inches from the
exposing area.  The tests on both papers took overnight to completely
clear of the brownish coloring.  From what I have read some people are
able to obtain an exposure on a light table in less then 10 minutes.  My
tests show a distinct separation between the Base+Fog of the pictorico and
the uncovered areas of the print up through 32 mintues.  On the Fabrino
paper with Ammonium Dichromate at 32 minutes this difference is just
barely noticeable and my thought is that at about 35 minutes I surpass the
base+fog of the pictorico.  After about 12 minutes on all test some
tanning is appearing.  If I were to go with a 35 minute exposure tanning
is sure to be visible.

My questions are:
1.  Should I try for longer exposures to see if I can obtain an exposure
sufficient to hide the Base+Fog of the pictorico and if so is there a
remedy to the tanning?
2.  Should I adjust my mix of sensitizer?  I have mixed the Potassium
Dichromate in a way that it has a large amount of precipitated chem unless
heated to almost 100F (this was done at a professor's request).  I mixed
the Ammonium Dichromate as outlined in Sarah VanKeuren's Non-Silver
Manual, placing chemical in a graduate to reach the 1oz line and adding
water to 10oz.
3.  Or do you have any other suggestions?

Thank you in advance for reading this long email and I am looking forward
to any words of wisdom you have to offer.

Best,
Jennifer Gioffre
Teaching Support Specialist

Architecture Art and Planning
Cornell University
120 Tjaden Hall
Ithaca, NY 14853
 
Office: 607-255-4207
Fax: 607-255-3462
jmg393 at cornell.edu
darkroommanager at cornell.edu