Laser irradiation—an effective means to create an anti-tarnishing surface on purple gold substrate

Purple gold(PG) hasemerged as a colored gold product for use in decorating jewelry items.However,PGpossesses little chemical stability in the ambient environments and undergoes noticeable decolorizing in a few months. This work uses the 4th harmonic Nd:YAGlaser as a newmeasure instead of conventional coating technique to generate an anti-tarnishing layeron PG.Thelaser beam brings about instant melting at the irradiated surface of PG and re-solidification of the melt leads to a dense overlaying thin layer, of which the structure is contingent on the laser parameters and thermodynamic properties of the treated surface. This thin layer possesses very different properties from the non-irradiated surface. An investigation of laser-irradiation effect by varying its scanning speed and scanning repetitions were carried out to determine an optimal treatment condition. In conjunction with this investigation, scanning electronmicroscopy (SEM),X-ray diffraction(XRD) and energy dispersive X-ray (EDX) were employed as well. The dependence of surface morphology and composition on the setting of parameters has been discovered through this work. # 2003 Elsevier B.V. All rights reserved