The Rowney Stay West palette works by osmosis. Acrylic colours dry solely by evaporation, but when applied to the membrane of a Rowney Stay Wet palette, the water lost by evaporation is replaced from the reservior paper. This enables you to paint all day with the colour uncovered. When nit in use, cover the colours with the transparent lid as this will reduce evaporation and leave your acrylic colours moist and workable for days. Adding a little water to the reservoir will keep the colours moist and workable for weeks. There are full instructions and helpful hits. We only have one of this item in stock and the price includes post and packaging to Uk Customers.