pearls and ice boxes

The most benign method of bleaching is exposure to sunlight, which is effective in lightening some typical colors of freshwater mussel pearls. This was rediscovered in 1960's Japan after a parcel of freshwater pearls sent to India by Uda Pearl Co was returned. While being re-forwarded around India for 2 years in translucent airmail packaging, the peachy-creamy pearls had become brilliantly white. Freshwater pearl processors began modifying ice boxes, which were being discarded in large numbers following the introduction of affordable refrigerators, with light bulbs to simulate the process. This kind of bleaching appears to have little or no detrimental effect on pearl lustre.