For acrylic painting, the Daler-Rowney Stay-Wet Palette will keep acrylic paints moist and workable for weeks. Its clear-lidded plastic tray contains three sheets of reservoir paper and 12 sheets of semi-permeable membrane paper. It's perfect for artists who want to keep their mixed palettes for an extended period of time.
Stay-Wet works by osmosis. Moisture evaporating from the surface is replaced by water from the dampened reservoir paper beneath the semi-permeable membrane which forms the working surface of the Stay-Wet Palette. The acrylic paint does not travel across the membrane, so it stays on the top of the membrane paper.