This is topic pigments that change color when ground in forum Art and Theology at Iconofile Forum.

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Posted by S Kane (Member # 7323) on :
I've just started water dispersing pigments with a glass Muller and slab that has been treated with 400 grit. Some of the colors change when ground; my cobalt becomes whiter, caput mortuum becames warmer, malachite bluer ect.

My question to more experienced painters is this: How do you preserve the original color of the pigment? Do you have another slab ground with different grit? Or do you add the pigment dry to the egg emulsion?
Posted by George (Member # 1) on :
Some pigments change color when dispersed in the binding medium due to the differences in the refractive indices of air when they are viewed as a dry powder and that of water when they are seen in the dispersed form.

Additionally, some pigments change hue slightly when ground to finer particles sizes. However, this is unlikely when grinding with a muller, because this instrument does not typically result in smaller particle sizes.

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