The possibility of giving artificial colours to Precious Stones was not unknown to the Romans. Pliny relates that recipes ware offered for sale which professed to turn Rock-Crystals into Emeralds and other transparent gems ; that in India many Precious Stones were produced by dyeing Rock-Crystal, and that the Ethiopians deposited the pale Carbuncle in vinegar for fourteen days, when it was alleged that it would shine brilliantly for a similar number of months.
Respecting the artificial colouring of certain Agates, Pliny says that in his day more of these stones were probably coloured artificially than naturally : and that in Arabia the Agate-nodules, if cooked seven days and seven nights in honey, will, when prepared by the artist, present veins, stripes and spots, which increase their effectiveness as ornaments.
This notion of honey purifying the Agate seems to be the foundation of the following beautiful idea : " All kinds of Precious Stones, cast into honey, become more brilliant thereby, each one according to its colour, and all persons become more acceptable in their vocation, when they join devotion with it : household cares are thereby rendered tranquil, the love of husband and wife more sincere, the service of the prince more faithful, and all kinds of business more easy and pleasant."—Extract from the Introduction to " The Devout Life" by S. Francis de Sales. Chap. III., par. 13. 1708.