I know Bernard was quoting.
In general it is best not to over complicate things.
Find something that works for you and stick to it until the light dawns and
something better comes along.
Flakiness arises in gum printing when the coating is too thick or if opaque
colours are being used that do not allow the light to cause the required
reaction.
Solution: use a light that is designed for use with graphic materials. A
high presure mercury lamp that peaks at the appropriate wavelengths is
best. It may be somewhat slower than a blast of light from tubes but the
analogy of cooking a roast applies; High heat cooks the outside quickly but
leaves the inside uncooked. Slow even exposure at the right wavelength
produces the results.
It is also better to avoid trying to achieve more than 0.7 density range
for one coating if you want good gradation.
Gloy is one way of avoiding flakiness for those who can get it. It gives
far more consistent results than gum arabic.. If you are having real
problems with gum arabic, and you cannot get Gloy, try albumen instead.
Incidentally 17 B gum gives consistently better results than the lighter
lithographers gums for gum printing. N cc of cold water added to N g
of white gum arabic powder and left to dissolve will give good results.
As to glass quarter inch or 5 or 6 mm plate glass will give good results
across the board.
Terry King
Terry king