I have been using commerically prepared lithographer's gum arabic for many
years. A galleon of this stuff lasts a long time and has the advantage of not
requiring any additional preservative. This gum is 14x Baume and for some
this may be too thin a gum and will require more size on the paper as well as
hardening of the size. Don't be afraid of using this type of gum just
experiment with it and find what type of paper, size , hardener, and pigments
will work best with it. What I have found is that if you try to follow what
someone else has found to work you MUST follow it exactly. For example, if
you use Steve Anchell article as a guide and he recommends making your own
gum but you use commerically prepared gum don't expect the process to work
even if you follow all his other recommendations to the letter.
Gum bichromate printing is by it's very nature subject to many variations (
paper type, concentration of dichromate, size, hardener, pigment, water etc.)
change one or more can make for splendid successes or dismal failures.
Unfornuately it is as hard to known why something works as why it fails. Try
to change only one variable at a time and keep experimenting until you get
the effect you want.
Larry Shapiro