Here's some business for the list:
I have a question regarding sizing for gum bichromate, and yes, I have read
the archive and followed some of the suggestions which have improved the
following but not totally eliminated it. It seems that no matter what I do,
I always have some slight staining of the paper. I'm wondering if it is
possible to size the paper in any way to TOTALLY prevent staining using
autodevelopment. It is not much, perhaps just barely noticeable as outdated
silver paper may exhibit slight age fog which prevents the true whiteness of
the paper base to show through. Am I asking too much? Should I lower my
expectations?
I really don't know if I can do better. I seem to be the only around my area
trying to do the autodeveloped gum thing and not manipulating the negative or
print in any way, so I have no local basis for comparison. To the best of my
recollection I don't think I've ever seen a nonmanipulated gum print with
absolutely clear highlights. Do they exist? If so, how do you get there?
Currently I'm having the best results using Lanaquarelle 140# HP sized with
2pkgs Knox per liter followed by hardening with the standard formaldehyde
bath. I use powdered pigments, saturated ammonium dichromate and prepared
14B gum arabic. Exposures range from 1-4 minutes in sunlight depending on
the pigment. And, once I've completed the image, I clear the dichromate from
the print in potassium metabisulphite.
Things I haven't tried are gloy and preparing the gum from powder. Will
adopting these prevent the very slight stain?
Things I have tried are the pigment stain test according to Crawford, etc.,
(which I've found to be inaccurate since the sensitizer does affect the
coating properties/viscosity of the solution) . I've tried more and less
concentrated gelatin sizing, single vs. double sizing/hardening, gesso at
various dilutions, using unpigmented sensitized gum to size by tanning,
glyoxal instead of formaldehyde, prepared high quality watercolor pigments
instead of powder, BFK, Fabriano, Arches and other recommended papers,
extending the development until absolutely no pigment is evident in the
water, and all permutations of the above. The slight stain persists.
One thing that has improved the staining problem is that I now use a
stronger, not weaker, pigment to gum+sensitizer ratio. I seem to get less
staining doing this (contrary to what many books state) since I believe the
more viscous emulsion sets quicker preventing the pigment to migrate into the
paper fibers.
I'm beginning to feel a bit like "Mary Hartman, Mary Hartman" wondering what
can be done about that buildup. Can anyone help me with this? There seem to
be so many variables affecting this process. Does anyone have a surefire
method or recipe for unmanipulated gum prints?
Thanks in advance for your help.
Joe