One of the problems  facing acrylic artists is that this type of paint often dries out too quickly.    Artists who work in acrylics ( as I do, albeit occasionally) know how frustrating it is when you leave a specially mixed colour, for even a short time, to find on your return, that the paint on the palette, is now as hard as a rock,  totally unworkable and, therefore, quite useless……

      Having seen artists try to keep their acrylics moist via the use of cling film,  kitchen foil and assorted covers, which worked for a couple of hours but not much longer, I have a solution that works very well, even in the summer heat of my Breton Studio.   That is, to place the palette, plate, and so forth, on which you have mixed the paints, in a (preferably) clear plastic box that has a tightly fitting lid.    This container will keep the acrylics moist and totally useable for several days.   I use the container for a brand of chocolates (covered in gold foil) that are extremely popular at Christmas, for this purpose, and it has never let me down.   I hope this tip will be of use to you.