Glass Pigment Mullers...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 approximately 1-5/8" the small one has a bottom diameter of approximately 3" the medium diameter is approximately 3-1/2" and the large diameter is approximately 4-1/2". Please note that due to the hand made nature of these mullers the bottom diameters may vary slightly- no two are alike!