Varnish Curing

Varnish is a combination of a resin, drying oil and a solvent. It is transparent and has no pigments. 
Varnish forms a film over the object and hardens once the solvent evaporates. Factors such as heat, humidity, type of oil, ratio of oil to resin affect the drying and curing of varnish. 
Exposure to infrared speeds up the process. IR penetrates through the varnish and heats the base quickly to fasten the curing process and ensures even drying.