Wax
The final treatment is a very high-carnuba wax. I prefer a floor wax called TreWax. It is available in Indian Sand, a reddish-brown formulation which goes particularly well with the woods used in Bear Meadow dulcimers, and in Clear, to be used on spruce tops.
Apply with lintless small cloth (2"x2") and keep a supply of small flannel cloths for wax rub out.