Chemical Bleaching of Wood and Its Aging : An Investigation of Mahogany, Walnut, Rosewood, Padauk and Purpleheart

Sammanfattning: This paper investigates chemical bleaching of wood and its ageing to make specie specific recommendations on which bleaching solutions to use when color adjusting veneer for furniture restoration.  In more detail, chemical bleaching of European walnut (Juglans regia), Rio rosewood (Dalbergia nigra), purpleheart (Peltogyne spp.), Honduras mahogany (Swietenia macrophylla) and padauk (Pterocarpus spp.) has been investigated using eleven different bleaching solutions. Both oxidative (e.g. hydrogen peroxide and potassium permanganate) and reductive (e.g. oxalic acid and sodium bisulfite) solutions have been used. Furthermore, to investigate aging of the bleached surfaces they were subjected to sunlight behind a glass window until a change in Blue Wool Scale 3 was obtained. Visual examination has been used to rank the color change after the chemical bleaching and the sun light exposure experiment. A small color change after the sun light exposure experiment indicates a high degree of lightfastness and is preferred for long term stability when restoring furniture. The results show that the wood species react in different ways to the investigated bleach solutions and to sun light exposure. It can also be noted that all investigated solutions were not suitable for all wood species. Moreover, the sun light exposure experiment identified effective bleach solutions that gave an unacceptable low lightfastness for mahogany and padauk after chemical bleaching. Based on the chemical bleaching and sun light exposure results, preferred bleaching solutions are recommended for the investigated wood species.