From: Jack Brubaker (jack@jackbrubaker.com)
Date: 04/15/03-10:55:43 AM Z
Dave,
I believe you are doing a good job of mixing the gum and pigment and that it
prints well but I doubt that you are really seperating each grain of
pigment. I was taught to make my own etching inks by grinding pigment into
oil. It took nearly an hour of serious physical work with a muller to get
all the pigment wetted with the oil. The machines that grind paints and inks
run the mix between steel rollers that are turning in opposite direction.
An opperater feeds the mix back through the machine sereral times over the
course of one to three hours for the finest product. I know we don't need
that quality. But mixing as we do we achieve a solution that is between
having the large clumps that scratch the size and cause print problems and
the fine grind of tube colors. I still think that the refined small clumps
of pigment of aggressively mixed gum-pig are contributing to the good print
quality many report with using powdered pigment. The small pigment clumps
are less likely to get into the fiber and not wash out than the finely
ground tube color.
> From: Dave Rose <cactuscowboy@attbi.com>
> Reply-To: alt-photo-process-l@skyway.usask.ca
> Date: Tue, 15 Apr 2003 07:40:15 -0600
> To: alt-photo-process-l@skyway.usask.ca
> Subject: Re: Mixing a light pigment for gum
>
> 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" <jack@jackbrubaker.com>
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Monday, April 14, 2003 11:40 PM
> Subject: Re: Mixing a light pigment for gum
>
>
>> 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
>
>
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