From: Katharine Thayer (email@example.com)
Date: 04/19/03-02:07:49 PM Z
Jack Brubaker wrote:
> As to consistance of powdered pigments...
> The earth colors are a lot like the ingredients my potter friend uses.
> makes all his clay bodies from scratch, buying industrial grade clays and
> bulk ingredients that he mixes together to get the clay quality he wants.
> Every few years a company will close a mine or go out of business. Each time
> he has to change to the "same" product from another provider his whole
> chemistry changes and he must try several suppliers and alter the mix to
> approximate the same result. The suppliers all claim that their product is
> the try material and the same as the classic ingredient.
The earth colors are a special case, more variable in some ways than
some of the other kinds of pigments, but they are still more the same
than they are different, and most importantly, the fundamental chemical
composition of a given earth pigment is the same wherever it comes from,
which was my point. Raw sienna is iron oxide, burnt sienna is roasted
iron oxide; raw umber is iron oxide plus manganese; burnt umber is
roasted raw umber, and so forth. You're right, there are slight color
differences depending on where the material comes from, due to trace
minerals and other factors, but the trace amounts of extra materials
aren't enough to change the fundamental nature of the pigment from one
source to another. Burnt sienna is burnt sienna; in spite of slight
differences in color and handling most artists can recognize burnt
sienna by sight and feel no matter where in the world it came from or
what paint manufacturer packaged it. Same with raw umber, burnt umber,
Earth colors are
> subject to the local nature of their origin. Each will have different trace
> elements or be similiar looking but utterly different chemically.
This last statement is incorrect, unless you are referring to earth
"colors" rather than earth pigments, in which case you're right, there
are colors that appear similar but are made from different pigments.
Different pigments are different chemically; the same pigment is the
same chemically, that's what makes it the same pigment. I don't
understand why this is so hard for people to grasp.
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