Discoloration of Furniture Finishes

Discoloration of furniture finishes was predicted by testing samples divided into two groups: Group 1, for testing individual components in a system – wood, stain, toners, sealers, lacquers, and contaminates; Group 2, the complete system itself – wood through rubbing. Group 2 involved testing of 6 by 12 inch panels of six species under six exposure conditions. Face veneer from the same piece of walnut, mahogany, maple, oak, prima vera, and avodire were used. Each panel was divided into eight 1-inch strips covering eight conditions: 1) bare wood, 2) filler over bare wood, 3) stain and toner over bare wood, and 4-8) complete systems with amber lacquer, pale lacquer, white lacquer, white lacquer and contaminates, and white lacquer with 1 percent additive. Panels were prepared after initial screening of Group 1 samples. The Group 2 panels were exposed for periods of 3 and 6 months from August to February to seven conditions: 1) an a range of exposure in northern climates, 2) an average of conditions for furniture exposed to diffuse light, 3) control, (wrapped in foil and paper at room conditions), 4) carbon-arc reproduced ultra-violet radiation, 5) sun lamp reproduced ultraviolet radiation, 6) exposure to sunlight in Florida, 7) exposure to 140?F. for 3 days then exposing panels as commonly wrapped or packaged to 110?F. and 80 percent R.H. Changes in wood and finishes under ultra-violet could be predicted. Stain, filler-toner, and even a clear, light stable lacquer each used alone slowed down wood discoloration rates, and combinations of these had a cumulative effect. A lacquer that yellowed under ultra-violet greatly reduced wood discoloration. Wood discoloration under a light stable system was gradual compared to any other factor causing discoloration, such as lacquer, contaminants, or bare wood alone. All stains faded when exposed to ultra-violet light. The addition of filler over stains and addition of lacquer greatly aided stain color retention. Toners are very light-fast when properly formulated. Toners provided the best protection for wood. The more toner used (color permitting) the more light stable the wood strata. Fillers tended to bleach lighter, and they required light-stable pigments. Filler alone did little to prevent discoloration, but when combined in a finish system it had a cumulative effect. Sealers afforded little protection for wood. Water white and pale lacquers did not discolor when exposed to ultra-violet light and heat; pale or amber lacquers discolored under these exposures. Most frequently, discoloration problems are due to an improperly selected lacquer or contamination of lacquer films. Contamination is best prevented by using the proper finishing system in manufacture.

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