About 20 years ago I purchased a couple of these great watercolour palettes, and although they look a little paint stained they have held up amazingly well. They are made of a lightweight, durable plastic, and the bottom part has 24 deep wells and 2 large mixing areas, and the cover has 4 large mixing areas. The cover fits snugly over the bottom though it’s not completely airtight. The dimensions are 11x16x1 inches.
I keep one for watercolour and the other for gouache, and I usually squeeze the paint into a well and I let it dry into a cake. I add a drop of water into the well when I’m working, and since I’m always working with these palettes the paint doesn’t go bad. As a watercolourist I find these palettes to be one of my most useful tools.