Optical and Material Science Properties of Aranmula Metal Mirror from Kerala

Aranmula mirror is a typical speculum metal mirror, cast and polished according to traditional techniques from Kerala in Southern India. We report our experimental investigations on detailed elemental chemical compositions, chemical surface structure, surface morphology, thermal stability, and optical reflectance of Aranmula metal mirror. The results of EDS based elemental chemical composition studies at the reflecting surface of cast, thin film coated and powder form of mirror samples have revealed the use of Arsenic (As), Silver (Ag), Gold (Au), Iron (Fe), Phosphorous (P), Sulphur (S) and Zinc (Zn) as minor constituents in Aranmula mirror making. The detailed surface structure and morphology of the mirror sample is studied for the first time using XRD and AFM. The Combined use of EDS, AFM and XRD analysis of the mirror samples reveal the presence of a transparent, non-metallic, corrosion resistant, smooth, nano structured thin film layer mainly consisting of a tin enriched delta phase (Cu31Sn8) on the mirror surface, which is amorphous in nature. It also suggests that Aranmula metal mirror contains nanoparticles that are considered to be quasi-crystalline in nature. We could prepare thin films of cast Aranmula mirror material with significantly higher optical reflectance for the first time. The average optical reflectance of the cast Aranmula mirror sample in the visible region is found to increase by 10 % when it is prepared in the form of thin film.