It scratches all substances and cuts glass; simple refraction; surpassingly brilliant, and being pure carbon burns without leaving any residue.

In the rough state it nearly always shows a few facets suggesting its true octahedral form with curved facets. Its specific gravity is the same as that of the topaz, which is less than that of the corundum and of the jacinth or hyacinth, but in hardness it surpasses all other gems.

Most diamonds are colourless, though not unfrequently tinged with yellow, pink, orange, blue, green, and even black or brown, these last being known to the trade as "Savoy diamonds." By the ancients the diamond was used in its rough state, embellished with its facets and natural angles alone. It even received the name of adamant, that is, unconquerable, owing to the supposed impossibility of cutting it artificially. In the time of Pliny it was already known that it possessed the property of cutting the hardest stones, and that it could itself be cut by means of its own dust. But for a long time no application was made of this discovery, because it was not known what mathematical combinations were required to give it its utmost brilliancy. At first it was table-cut, much labour was expended in this way, and the irregular facets so produced imparted less effect than that of a simple piece of rock crystal. At present it is cut into two forms. The brilliant shows on its upper surface a large plane or "table," surrounded by a multitude of facets forming the so-called "dentelle" and named according to their various forms. The lower portion, which should be half as thick again as the upper, terminates also in a plane surface, connected with the dentelle by a number of facets called "pavilions." The rose diamonds are stones of small size, forming, instead of the dentelle, a pyramid with numerous facets.

The Flagellation. The figure of the Saviour in redljasper, the purple veins of which have been worked into drops of blood. The pillar is of rock crystal, and the pedestal of chased and enamelled gold.

Beginning of Seventeenth Century. (Louvre).

Most works treating of the diamond credit the discovery of its cutting to Louis de Berquem of Bruges, who is supposed to have practised the art so early as the year 1476 (1475?). But the Marquis de Laborde has shown that this is evidently a mistake. In 1407 there was flourishing in Paris a renowned diamond cutter named Herman, and in 1465 in a dispute on the subject of an amethyst sold as a balas ruby, there occur in Bruges the names of the experts Jean Belamy, Christian Van de Seilde, Gilbert Van Hissbughe and Leonard de Brouckrre, all diamond cutters. In his description of Paris, under the date 1407, Gilbert of Metz refers to "la Courarie where reside the workers in diamonds and other stones." Lastly, in 1416, the inventories distinguish between the recent diamonds with their natural facets (pointes naives) and those cut in tables, scutcheon fashion and "mirouers".

The same uncertainty prevails as to the date of diamond engraving. According to most writers Jacopo da Trezzo, a Milanese, who flourished about the middle of the sixteenth century, was the first so to treat this refractory stone. Mariette assures us that it was Clemente Birago, a contemporary artist, who essayed in 1564 to transfer to the diamond the effigy of Don Carlos, Infant of Spain, a work intended for his betrothed, the Archduchess Anne, daughter of Maximilian II. Others again assert that so early as 1503 Ambrogio Caradosso had engraved the figure of a Father of the Church on a diamond belonging to Pope Julius II. It would be difficult now to decide this question, but it is at least certain that Jacopo da Trezzo engraved fine stones, notably a garnet with the busts "affronte" of Philip II. and his son Don Carlos. Later on Natter and Costanzi practised diamond engraving.