BORT CARBONS, ETC.
	one of those ancient arts which were later lost, for con­clusive evidence does not exist of engraved diamonds earlier than the sixteenth century. It seems probable that either the " Jahalom " of the breastplate did not signify diamond, or if it did, that the stone was one of similar appearance only and not what it was supposed to be, for all the engraved diamonds known, have come to knowledge since the date generally set for the dis­covery of the art. It is said that Jacopo or Como da Trezzo, or his pupil, Clement Birazo, discovered the art of engraving the diamond at Milan in 1556. According to Blum, Ambrosius Caradossa was the first to sculpture it. A specimen of Jacopo da Trezzo's work, set in a ring, was exhibited in the Italian section of the Paris Exposition of 1867, and another by the same artist, on which the arms of Charles V are engraved, is in existence. Streeter says that the Duke of Bedford has one with the head of the philosopher Posidonius. He also mentions a portrait of the Spanish prince, Don Carlos, by Clement Birazo; the arms of Queen Mary of England by Jacobus Thronus; a signet of Mary of Modena, Queen of James II, with an interlaced cipher M. R. surmounted by a crown; five fine examples, of which four are signets, in a collection at Florence, consisting of one which be­longed to Catherine de Medici, with the monogram M. C. and a coronet; one with the Medici shield crowned; one with the crowned arms of Portugal and another small one with a shield, arms and coronet. Three in the Hope collection have the portrait of a philosopher, the head of Emperor Leopold II and one with an en­graved cross. A thin stone with the head of Napoleon 22