Resins dissolved in liquids for coating wood or metals, drying to a transparent, shiny, hard film. Epoxy-based varnishes are widely used to lacquer the inside of food cans, where the coating blocks contact between metal and food — preventing corrosion, metallic off-flavours, and hydrogen swells from acid attack. Interior can coatings must meet food-contact regulations, with migration limits on monomers such as bisphenol A pushing reformulation toward BPA-non-intent alternatives. Coating integrity — free of scratches, blisters, and porosity — is verified during can manufacture, since any breach invites corrosion and spoilage.