How do you stop the paint drying too quickly during a long session?

To stop your acrylic paints drying out too quickly during a long session, use a wet palette (a palette with dampened kitchen paper covered with greaseproof paper, or a purpose-made stay-wet palette). Only squeeze out the amount of paint you need each time and keep the pots firmly closed. Lightly mist your mixes with a water spray bottle as you work. Avoid painting in a room that is too hot, too dry or in a draught, and choose a room at a moderate temperature (around 20°C) with normal humidity. For particularly long sessions, invest in an acrylic retarder medium that you can mix into your paints to slow their drying time considerably without altering the colours.