Glass is a wonderful surface to mix paint on. Very slick and durable, it won't absorb oil or water and is a snap to clean. Perfectly sized to fit Sienna Plein Air Pochade Boxes, these inserts are made of tempered glass, much stronger than regular glass. Their edges have a smooth finish for safer handling and cleaning. Choose Medium or Large to coordinate with your pochade (one Large Palette Insert is included with the Large Pochade Box, but may also be purchased separately).