In order to understand the effect of varnishes that act as a barrier to water adsorption by wood - in terms of moisture content - in humid atmospheres, modern maple replica samples have been manufactured by a practicing luthier. They are coated with a variety of recipes thought to have been used in either the original manufacture from the 17th to 18th centuries, or in subsequent restorations. The effects of humidity were monitored via thermal neutron radiography using the NEUTRA imaging instrument at the Paul Scherrer Institute. The consequences for understanding ancient violins, and their repair or restoration are discussed.