Benvenuto Cellini, The treatises of Benvenuto Cellini on goldsmithing and sculpture (1898)
“ The peculiar virtue of the diamond, however, admits of the trying of a simple experiment, by which you can at once distinguish one stone from another, and it is this. You take your tint & rub both stones with it; your true diamond grows in brilliance & beauty, the other becomes deadened and splendourless. And this test suffices without trying the test of hardness too, but if you rubbed the two stones together you would soon find out the diamond. Though the sapphire is so much harder than the ruby & the emerald, it is a thousand times less so than the diamond. ”
