Mediums are the key to the wet on wet technique.
The most important one and one you will probably use most of the time is Liquid White. Liquid white is included in both kits. But if you are buying paints on your own (or you need more) you ‘ll need to buy some.
Liquid clear is used when you start off with one of Bob’s famous black canvases.
Liquid Black is rarely used, but you might want to have it.
You can also buy a set of all three mediums.
Set of 3 Liquid Mediums