The 100-inch telescope mirror at the Mount Wilson Observatory in California was originally coated with silver. Silver,however,loses its polish easily,and it was necessary to replace the foiling twice yearly.

• 加利福尼亚州威尔逊山天文台的100英寸望远镜镜面原先涂的是银粉，但是银粉很容易失去光泽，因此每年都得重新涂两次。