<< I think the following are at least more independent (than the
traditional treatment of watercolor pigment, gum, and dichromate solution as
independent variables):
viscosity of gum
thickness of coating
microscopic toothiness of paper
amount of size
degree of hardening of size
hue of pigment
opacity of pigment >>
Oh, I forgot to type in also the following
* the amount of dichromate ion
* the amount of water (dilution of final mix)
The reason that these are important and must be considered independently is
because, for example, you can have 10 ml of 10% dichromate, or 20 ml of 5%
dichromate, and you have the same amount of dichromate ions, but you dilute
the mixture differently, thus affecting the viscosity of the mix (which affect
the pigment suspension), and the viscosity will in turn also affect the
thickness of the coating.
Dave S