Clean out cracks and holes and smooth the edges before filling. Melt the shellac with a heated steel knife. When hardened, shave off excess shellac level with the surface. Remove dark spots Remove dark spots by sanding or bleaching. Too severe treatment will remove the lovely quality that age has given the wood.
Commercial bleaches are available with clear directions.
Apply the solution with brush, cloth or sponge. Let stand 10 to 20 minutes. Repeat as necessary. Rinse with clear water. Oxalic acid is poison.