From: Jack Brubaker (jack@jackbrubaker.com)
Date: 04/14/03-11:40:50 PM Z
Chris,
I have thought on why some pigments stain when machine ground for tube paint
and don't when used as powder mixed by hand into our gum solution. Someone
was commenting last month about having read about grinding pigment into the
gum until it no longer clumps. I think the clumping refered to is the
tendancy of the finely powdered pigment to not easily disperse in the mix.
At first the powder will "clump" together with many particals of pigment
cemented together but dry inside the clump. The goal when grinding pigment
into any medium be it oil or gum or what have you is to wet each grain
seperatly. This can only be done by grinding very aggressivly with a solid
muller on a hard surface like glass of steel. However I doubt that anyone is
doing that for gum printing. So we are in effect printing with small clumps
of pigment not super finely ground pigment. I believe the finer the pigment
the more likely it is to sink deep into the surface of the paper or size and
not wash out during developement. Hand ground (or brush mixed) pigment will
be more likely to sit on top of the paper surface and be easy to develope.
In purely economic terms we are wasteing pigment doing this since the
pigment reaches its maximum tinting strength by being fully wetted out in
the solution (the grains are all visable not stacked behind oneanother).
Tube paint is finely ground to maximize the pigment and to keep it in
suspension. But, pigment conservation is not as important as getting a
print with clear whites. For reasons we can only guess at paint
manufacturers add other ingredients to their paints some of these may
further conflict with our goals. Most of my printing has been with tube
color but I am beginning to wonder about it...
The above is my guess as to what is happening. Does anyone have any thoughts
or experience that would shed more light on the subject?
Jack
> From: "Christina Z. Anderson" <zphoto@montana.net>
> Reply-To: alt-photo-process-l@skyway.usask.ca
> Date: Mon, 14 Apr 2003 21:50:26 -0600
> To: alt-photo-process-l@skyway.usask.ca
> Subject: Re: Mixing a light pigment for gum
>
> Dave,
> Do you notice a difference between ivory and lamp black? And
> quinacridone what? Cobalt what? Cadmium what? I have cobalt blue and
> violet but man, are they weak. In tube form, anyway. I did use a powdered
> q. violet the other day and it was incredible how it did not stain and yet
> was really bright, vs. the tube pigment which did. I can't figure out why
> that would be the case.
> Chris
> ----- Original Message -----
> From: "Dave Rose" <cactuscowboy@attbi.com>
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Monday, April 14, 2003 8:32 PM
> Subject: Re: Mixing a light pigment for gum
>
>
>> As others have noted, reducing the amount of pigment will produce a more
>> subtle effect.
>>
>> My favorites? Umbers, siennas, ochres, phthalo blues & greens,
>> quinacridone, cadmium, cobalt, ivory and carbon blacks. I prefer powder
>> pigment to watercolor paint.
>>
>> Dave in Wyoming
>>
>>> And maybe I can ask this--what are people's favorite
>>> colors--specifically paints? So far, for instance, in testing raw
> sienna
>>> against gamboge, similar colors (gamboge is yellower and more brilliant
>> and
>>> more transparent) I would choose raw sienna because it clears very well.
>>> Chris
>>
>>
>
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