Any staining fruit of vegetable can be used - beets, onions, blackberries, blueberries. Just boil in enough water to just cover the plant material - boil and then steep and the longer they steep the deeper the color. Over time this color will fade. Brush on, thet thoroughly dry and protect with oil or wax.

They have a transparent, not an opaque quality - light passes through the stain and is reflected off of the wood grain.