The glass palette insert is an accessory for the sienna plein air pochade box. There are two sizes of glass palettes available to match the two sizes of pochade box, (M and L). Glass is a wonderful surface to mix paint on. It is very slick and durable. It wont absorb the oil or water in paints. And it is very easy to clean. The palettes are made with tempered glass which is much harder and stronger than regular glass. The glass palettes also feature smooth finished edges making them safe to handle and clean. You can place white or grey paper under the glass (not provided) to aid in color mixing. Dimensions: The M glass palette insert measures 9" x 10". Fits Sienna Plein Air Artist Pochade Box Easel Medium.