Finishing Spirit is Ethanol. It is similar to denatured alcohol, but it is a more pure and higher quality thinner for shellacs. The Fiddes shellacs are all formulated with Finishing Spirit, and for times when a shellac needs to be reduced, e.g. from a three pound cut to a two pound cut, Finishing Spirit will maintain the quality of the shellac. Clean up of shellac brushes can be done with the less expensive denatured alcohol.