Shellac

Shellac is a natural resin, secreted by the lac insect and harvested from tree branches, dissolved in denatured alcohol to make a finish that dries by simple solvent evaporation, much like lacquer. It ranges in color from nearly clear (blonde/super blonde) to a deep amber-brown (garnet), depending on how the raw resin was processed, and cures food-safe enough to be a common choice for wooden bowls, boxes, and utensils.

Beyond use as a finish in its own right, shellac is the traditional universal sealer coat -- it sticks to almost anything and almost anything sticks to it, making it the standard barrier layer over knots or stains bleeding through, or between incompatible finish layers that wouldn't otherwise bond to each other. Its main practical weakness is limited resistance to water and alcohol, since it re-dissolves in exactly the solvent it was applied with.