How to Make Your Own Moisture-Retaining Palette for Acrylic Painting
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I wanted to buy one, but they are a little pricey. I would have made one, but I am far too lazy. Instead, what I have been doing is putting my excess paint leftovers in a Gladware sandwich container with a well-wrung-out damp paper towel along one edge, and it’s been working fine to keep that paint moist enough to use. Some of the paint has been in there since I got it a few weeks ago, and though it’s starting to get a little watery, it’s still perfectly usable.

Just a little FYI for anyone wanting to save acrylic paints for later usage.