Some material types, such as plaster, wood and various metals, traditionally have been painted and coated for surface protection, corrosion prevention and aesthetic coloration. Many metals, most commonly bronze, historically were patinated by application of corrosive patina solutions to induce desired color effects. When the desired colors were achieved, clear coatings were applied to preserve the color and to protect the metal from pitting and other surface corrosion loss. Over time, coatings fail, leading to visually disfiguring appearances, damage to patina, and substrate loss due to continued exposure of unprotected surfaces.
The conservation of coated objects requires an understanding of the substrate materials as well as the coatings used. Coating samples can be analyzed to determine the material types, layering sequences and historic colors. In many cases, particularly indoor fine art and historic objects, original surface coatings are integral to the overall object and should be conserved through consolidation and possible in-painting. Depending on the severity of the damage and historic significance, outdoor objects may require overall coating removal, appropriate surface preparation and reapplication of a new coating system. Bronze and other metals can require patination to unify disfiguring appearances and application of a protective coating appropriate for the location environment and future maintenance cycles.