DISCOLORATION OF OAK VENEER INDUCED BY METAL IONS

The 3 mm thick oak veneers were discolored by single ions of Fe2+, Cu2+, and Mn2+ and mixed ions of Fe2+-Cu2+, Fe2+-Mn2+, and Cu2+-Mn2+. The brightness (L*), red-green index (a*), and yellow-blue index (b*) of the veneers changed by varying degrees with the changes in ion mass fraction, temperature, heating time, ion species, and ion mass fraction ratio. The maximum values of total color difference (△E*) of the veneers were 38.94, 11.79, and 9.42 for Fe2+, Cu2+, and Mn2+. Moreover, the total color difference (△E*) values of 24.07, 13.71, and 4.45 were observed for Fe2+-Cu2+, Fe2+-Mn2+, and Cu2+-Mn2+ mixed ions. The veneers showed different degrees of vibrational peaks after discoloration. According to the ultraviolet spectrum, Fe2+ had a red shift in the ultraviolet absorption band of the unsaturated carbonyl compound and benzene ring compound. Moreover, the dark effect of Fe2+, Fe2+-Cu2+, Fe2+-Mn2+, Mn2+, Cu2+-Mn2+, and Cu2+ gradually decreased. The surface of the veneer was flat, without any rupture or deformation, and the pores were clear after treatment.