The substrate, in this case a 6 x 6" cut of wood (pine) needs to be porous for the wax to adhere.
Wax only works with oil-based paints and paint sticks, etc. Yikes - that was the first scary part. I've never worked with oils. Fortunately, also molding paste works with encaustic. The stencil in the upper left corner was created with wall spackle (100 times cheaper for the same result).
Layers of wax and color have been built up here. Lines can be incised into the wax while warm, creating more texture. The history of wax painting goes back to Egyptian times, and used throughout history, with a recent insurgence as of late.
The aroma of the beeswax is divine in my art room!