I use a home-made exposure unit of flourecent black-light tubes for consistant
exposures. I start by make a cyantype of my negative as a base to add gum to
or just as a proof to help gage the initial highlight exposure. By using a
10% potassium dichromate sensitizer solution (rather than the 30% most formulas recommend), the correct cyan exposure gives me a fairly accurate first exposure
for the highlights. This highlight coat should be relatively thin. Subsequent
printings are increased slightly in pigment concentration, or thickness.
Exposures are reduced by approx. 10% each printing. Printing goes as long as
necessary.
Early on I learned that it is very important to get a smooth coating, but very
very difficult to achieve (humidity effects greatly how the gum sets up). To
get a smooth coat I resorted to brushing sensitizer without gum onto the paper
and airbrushing the gum/pigment on top. This allows very precise control over
the thickness of the gum/pigment and allows fairly accurate control of
different colors without resorting to separations negs.
***Warning*** Don't spray the dichromate solution; you don't want to breath it.
Also wear a respirator when spraying the gum even though it is just particle
matter you are concerned with there.
Remember that successful gum printing is an empirical process that can only be
outlined. It must be learned by each individual based on the numerous variables
and conditions of their personal printing habits and space. Good luck in the
search.
Shane
-- ********************************************************************************Shane Patterson Dept of Visual Arts College of Architecture patters@hubcap.clemson.edu Clemson University Home (803) 287-5320 Office (803) 656-3924 ********************************************************************************