<< Dave, I don't find pigment concentration a factor in staining.... try it
yourself.... double the pigment in a mix and see if you get more staining.
>>
Hi Judy,
No, if I double the pigment in a mix, it is true that I don't get more
staining. :)
But unless we are looking at very old books, most modern book use "pigment" in
the place of watercolor or gouache mix. Watercolor or gouache is already
pigment suspended in gum. In particular, watercolor is made to be greatly
diluted, so the gum used might be more viscous (higher Baume?) that the gum we
use in gum printing, so the pigment is very well suspended there, so when I
add more watercolor "pigment," the suspension of pigment in gum is not
affected much (it might even be improved), so I won't get more staining.
But this is a good example of the mutli-variable (or multi-dimensional) system
that I mentioned. When we say we add more pigment, we are not adding just more
pure pigment. We are actually adding pigment *and* gum, so if nothing else
change, we actually get thicker mix (because more gum but same amount of
dichromate / water). More pigment will affect the tonal scale, but more
viscosity will affect the physical scale (how thick the gum can be on the
paper), and they affect each other in the final appearance.
Same thing when we say adding more dichromate. We think of the dichromate as
*one* variable, but it is not an *independent* variable. In particular, when
related to gum printing, adding the dichromate increases the amount of
dichromate ions, which affect the hardening of gum, but it also adds water,
which affects (or can affect) the viscosity of the mix and the thickness of
the coating.
Of course, the final image is also affected by the texture of the paper. By
that, I mean the microscopic tooth (e.g. comparing a magazine paper with a
newsprint), not the macroscopic texture (e.g. comparing rough watercolor paper
with Mi-tentis paper). The macroscopic texture has some effect but is easily
predictable.... nothing real mysterious there.
and of course the sizing.... which depends on the amount of gelatine and the
degree of hardening.
and of course the actual pigment.... which depends on the hue (which end of
the spectrum) and the opacity and maybe even the coarseness.
What I am trying to say is that most book do talk about some tests by changing
one "variable", but they do not realize that those variables are not
*independent* variables. The result is that one can find a particular formula
for a particular paper, particular sizing, particular pigment, particular
coating, etc. that works, but one cannot fully understand the physical process
and apply that to another situation. And that's why for each different
situation, we must start almost from scratch again.
Of course without knowing all the physical characteristics, we cannot be sure
which ones are independent (it's the chicken or egg question, which one comes
first), but so far (from my tests and some hypothesis to be proved or
disproved), 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
I am structuring my tests to handle these variables. I don't mean that
gummists will need to have special equipments to measure this, but at least in
a practical way, we still can better understanding and control of the
independent variables. When doing these kind of tests, I am indeed paying the
cost of not having much time to do my own artistic work, but I hope that some
day I will be able to contribute something in gum control.
And since it seems that people are a little tensed lately, I want to say that
I am not saying that I know the most or my theory is right or whatever, I am
just describing my tests and my approach. You can agree or completely
disagree, but please don't flame me. :) And you noticed that I sometime
describe things as "models." That's a term often used in engineering. With
that I mean, I don't have all the expensive equipments to measure every
parameter and to observe the microscopic structure of paper, mixture when wet,
mixture when dried, thickness when wet, thickness when dried, etc. etc. so I
don't *exactly* know what is going on physically, but usually you can have
your model (or theory) that explain things well.
So far (this is actually revealing my secrets a little bit), my hypothesis or
model can explain things better than those commonly described in books (we
don't have many that really deals with what is happening physically,
micorscopically anyway) and can even explain some data or evidences that seem
contradictory (it usually means that the "model" is fairly accurate). When I
find more time (oh, how can we find enough time?) I will do more tests and let
the list know of my finding.
Sincerely,
Dave S