I put my maiolica over glazes in old watercolor trays so that I can mix colors. This also allows me to save the color for continuous use day after day. The trays all have lids, so that I can just keep wet them down before wrapping after using for a day. I also put a damp rag in the container to keep them moist. The next day the colors are ready to use. I have two trays, one with cool colors and one with warm colors.