Re: Ball milling pigments
Alex Nanson (alec@norlex.demon.co.uk)
Sat, 27 Jul 1996 21:08:24 +0100
In message <Pine.SUN.3.91.960726222634.23090C-100000@panix2.panix.com>,
Judy Seigel <jseigel@panix.com> writes
>
>OK, here I am, the wet blanket again. But something else occurred to me ....
>
>Richard Sullivan wrote:
>
>> The possibilities
>> are: more or less contrast, more or less transparency, more or less
>> resolution, and probably others. I assume that the answers cannot be derived
>> with any accuracy without some practical experience or experimentation with
>> pigments of varying corseness. I am curious about this because that I have
>> considered the possibility of making and selling superfine ball milled
>> pigments for gum.
>>
>
>"Superfine" pigment might act like dye -- be actually harder to get out of
>the paper grain. From what I know (& obviously all of us are familiar
>mostly with our own patch of the elephant), contrast is controlled by
>other factors (including tone of the color itself, absolute amount of
>pigment and proportions of pigment to gum to sensitizer) than grind, and
>transparency is a factor also of the chemical itself. And maybe superfine
>pigment could actually look hazier -- more surfaces to diffuse the light.
>(Like my crinkly reflector.)
>
>As for resolution, in my experience the major variable (assuming a good
>emulsion mix) is the grain of the paper -- and even the coarsest pigment is
>finer than the grain of even a fairly fine paper.
>
>Judy
I don't know enough about pigment processes to say how the pigment
fineness would affect the contrast etc., however, pigment manufacturers
control the particle size of their products to within fairly close
limits, and any attempt to further reduce the particle size by dry
grinding would alter the colour and probably lead to contamination of
the pigmemt by the grinding media.
It was my experience when employed as a lab assistant on raw materials
testing in the paint industry. That a consistant dispersion and hence
more reproducible results, with regard to colour, and covering power
etc., were obtained by ball milling the pigment in a standard medium,
rather than trying to disperse the pigment in the medium with a pestle
and morter. This particularly applied to the carbon blacks and certain
of the organic pigments.
Thus it would seem to me that it may be worthwhile to investigate the
effect on the final image by predispersing the pigment in some of the
gum by ball milling. Any good book on paint technology should provide
more detailed information.
Alex.
Alex Nanson
Gloucester UK