A wet palette is a sealed tray holding a water-soaked sponge under a semi-permeable parchment sheet. Acrylic paint mixed on the membrane stays workable for hours — with the lid on, for days — because moisture migrates up through the paper exactly as fast as the paint loses it.
It changes brush painting economics completely: mixed colors survive overnight, thin glazes stop drying on the palette, and you waste dramatically less paint. The one maintenance chore is changing water and paper before anything grows in it.
See it in context in our brush painting guides, or explore the tools hands-on in The Bench.