From: Dave Rose (firstname.lastname@example.org)
Date: 04/15/03-07:40:15 AM Z
It's essential to thoroughly mix dry pigment into the gum. If not mixed
well, small clumps of pigment will cause streaking and staining. I mix up
pigment/gum with a stiff bristle brush and/or an electric stirrer.
Dave in Wyoming
----- Original Message -----
From: "Jack Brubaker" <email@example.com>
Sent: Monday, April 14, 2003 11:40 PM
Subject: Re: Mixing a light pigment for gum
> I have thought on why some pigments stain when machine ground for tube
> 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
> 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
> doing that for gum printing. So we are in effect printing with small
> of pigment not super finely ground pigment. I believe the finer the
> the more likely it is to sink deep into the surface of the paper or size
> not wash out during developement. Hand ground (or brush mixed) pigment
> 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
> or experience that would shed more light on the subject?
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