Among variables for gum exposure are proportion of gum to sensitizer, the
paper, the thickness of the coat (light has to get through it), the color
(red through yellow are less sensitive to UV light), denseness of
negative, drying method (forced heat-drying reduces sensitivity,
depending on handling up to a factor of five!) and age of sensitiser.
Also, Gini may be using ammonium dichromate, which is a more saturated
saturated solution than potassium.
Judy