I understand that the colors on anodized aluminum may derive from metallic salts or from organic dyes. How lightfast are these colorants in an indoor application?
Generally speaking, organic dyes are well suited to indoor applications and have enjoyed such use for over 50 years. Their light-fastness, however, depends on the dye chosen, the amount of dye that is actually contained by the coating, and the conditions of seal. Two-step electrolytic coloring uses metallic salt solutions to produce bronze or black colors that are sufficiently light-fast for exterior, as well as interior, applications. Colors produced using organic dyes are often susceptible to change due to the effects of ultraviolet (UV) rays from sunlight. However, they should be satisfactory in indoor applications where they are not exposed to sunlight. Some organic dyed anodized aluminum can show significant color change within one year of outdoor exposure. If we assume that is 10 hours exposure to sunlight per day, then indoor finishes may be able to withstand one hour of sunlight per day for 10 years.
