Glass Pigment Muller - These mullers are hand blown glass. The bottom of each one is ground so that the glass is matte; allowing for smooth pigment grinding. They are meant to be used with a glass palette, for grinding powdered pigments into your own paint. Use them to make your own oils, egg tempera, even watercolor; by grinding powder pigments into your own selected binder. The mini one has a bottom diameter of 1-5/8 inches, the small one has a bottom diameter of 3 inches, the medium diameter is 3-1/2 inches, and the large diameter is 4-1/2 inches. Please note that due to the hand made nature of these mullers, the bottom diameters may vary slightly.