In this case, one of two things has happened. Either the shellac finish is scortched or moisture has gone through the finish into the wood. If we assume that the finish is discolored by heat, then Wood Elixir applied with steel wool can substantially reduce the offending mark. Wood Elixir is designed to remove contamination from the surface of the finish while strengthening the original finish. If the mark is in the wood then Wood Elixir will not solve this. The bare wood must be bleached.