The pigment industry is huge. Repackaging is common and in the end you are
paying mostly for the handling and packaging. The pigments themselves are
fairly cheap.
Daniel Smith and other art suppliers should have a selection of powder pigments.
>>
>>Sounds interesting!!
>
>Then Dick Sullivan butts in:
>
>While we are on this topic, Jack Mac Donald, who used to run an Alt-Photo
>school in Inglewood California said that none of the prepared pigments like
>W&N were fine enough for gum. He claimed that Wm Mortenson (I can never
>remember how to spell his name)
It's Mortensen. Look him up in my Encyclopedia which I know you have...
>would buy dry pigment and ball mill it. This
>is a process where the pigment is put in a can with some 1 inch size ball
>bearings and the can rolled on a device similar to what rock hounds use to
>polish rocks. This process can take weeks I was told. My suspicions are that
>this is another one of those legends abounding in the photo world. Anyone
>have any knowledge of this?
I did a fair bit of research into this when I got seriously into pigment
printing. The industry uses basically two different types of mills: Roller
mills and ball mills.
Roller mills are used by manufacturers of watercolors and oil paints sold
in tubes. Picture this: Two steel rollers are practically touching each
other while turning in the same direction, but at *different speed!* You
pour your mixture of say, gum arabic/powder between the rollers where it
gets squeezed and sheared at the microscopic level. Don't stick your finger
in there! Depending on the nature of the pigments and the desired quality,
the process is repeated 2 or 3 times. This is how they make thick
dispersions that you buy in paint tubes. The steel rollers btw have to have
cold water run through them because of the tremendous heat generated by the
friction. This tends to create condensation on the rollers and...
I came close to buy one, rebuilt, but it was still in the thousands of
dollars, so I ended up with solution #2:
Ball mills consist of a special ceramic vessel (hardness rating #9, if
memory serves, on the Mohs scale; #10 being diamond grade) in which you put
your emulsion and either steel or ceramic balls. You put the cover on it
and lay it on its side between two rollers specially shaped so that when
you turn on the motor you can leave it unattended as the vessel won't have
a tendency to walk away on its own. The heavy-duty unit I bought was less
than one grand I think. It's built so you can leave it run 24 hours a day
all year around if required. At the beginning I experimented with runs of
several hours to several days but in the end, with the pigments at hand, 15
to 30 minutes was all that was required. This type of mill, unfortunately,
will not give you a thick paste like you can squeeze out of paint tubes. It
provides a highly concentrated liquid dispersion, called "toner" in the
industry.
The actual process is more complicated than it sounds... The size of the
balls, their proportion in relation to the amount of emulsion, the type of
pigments, the pre-dispersion mess, the inevitable spills, etc. are no fun
at all. This is one of the reasons why carbon is less popular than Pt/Pd
printing.
Those who want to know more may want to look up my _Modern Carbon Printing_
and check the references.
Luis Nadeau
awef6t@mi.net
Fredericton, New Brunswick, Canada
http://www.mi.net/dialin/awef6t/