Can you mix tempera and acrylic paint?

No! Don't do that! Acrylic and Tempera paint don't mix whatsoever. Although both paints are water based, tempera contains chalk, casein (a milk product), and often times egg making the product more loose and easier to use. Acrylic on the other hand is a thicker more stable paint that contains a plastic blinding ingredient that makes it oilier and more permanent! Don't mix the two, it will turn out bad I assure you.