To use a moisture-retaining palette, first thoroughly soak the sheet of watercolor paper with clean water and place it in the bottom of the palette. Dampen the piece of grease-proof paper and place this on top of the watercolor paper. Alternatively, place the two sheets in the palette, cover them with water, leave them to soak for a bit, then pour off the water.
Squeeze out a little acrylic paint onto the greaseproof sheet, as you would on any palette. If you place your colors around the edge, the central area can be used for mixing colors. If you're painting with a knife be a little gentler to ensure you don't tear the paper.
How Long Does Paint Keep?
If you ensure that the piece of watercolor paper in the palette doesn't dry out and place the lid on the palette when you're not painting, reducing evaporation, your paints should stay moist and usable for days. Like most things, once you've used a moisture-retaining palette a bit you'll learn to recognize when you need to add a bit more water to the watercolor paper.
The clearest sign is that the edges of the greaseproof paper start to curl away from the watercolor paper. If you need to re-moisten the waterproof paper, lift one corner of the watercolor paper, pour in a teaspoon or two of water underneath, then gently tip the palette so the water runs under the paper.
How Do I Clean the Palette?
Simply fold up the sheet of grease-proof paper and throw it away, rinse the piece of watercolor paper (this can be reused many times) and the palette itself.
I've had the paint and paper stay moist long enough to go moldy on a couple of occasions when I've forgotten to clean my small moisture-retaining palette in my traveling painting kit. I then give it a very thorough wash with washing-up liquid and leave it to dry in the sun.
