William Harrison, Holinshed Chronicles: England, Scotland…
“ I haue heard that the best triall of a stone is to laie it on the naile of the thombe, and so to go abroad into the cleare light, where if the colour hold in all places a like, the stone is thought to be naturall and good: but if it alter, especiallie toward the naile, then is it not sound, but rather to be taken for an artificiall péece of practise. ”
