If the technique is done properly, you should always have some leftover paint on your palette because Bob's methods require a lot of paint.  So, place used paint into sealed plastic containers, one for darks and one for lights (or each color can have its own container, those little canisters for camera film are good, or old ice cube trays covered), then into the FREEZER they go.

When you are ready to paint again, defrost for about 15 minutes.  Freezing the paint twice is probably the maximum; it'll turn hard when no longer usable.

Tip from Bob Ross Inc.