I work in acrylics and once they are dry — they are dry. My palette is a shallow plastic box with a tight fitting top. A spritz of water and sealing up the lid usually will keep the paints for a day or so. But sometimes when I reach a stopping point, I know some paint might go to waste. This is when an artist should reach for a piece of paper and work fast before making dinner. This example (9”x7”) was painted the other day from a springtime photo of the Inverness Ridge Trail at Point Reyes.