Tarnish behavior of low karat golds was studied quantitatively using a spectrophotometer. Color change expressed in CIE Lab system was recorded during tarnishing at various concentrations of ammonium sulfide solution. Tarnishing curves: color difference DE*, red-green coordinate a* and yellow-blue coordinate b* were plotted as a function at tarnishing time. It is shown that such curves fully describe tarnish behavior of karat golds particularly for jewelry applications. Effect of suppression of tarnishing by using some additives is demonstrated.

Author: G. Raykhtsaum and D.P. Agarwal