"In sculpturing ivory," says Theophilus, "first form a tablet of the magnitude you may wish, and superposing chalk, portray with a lead the figures according to your pleasure, and with a pointed instrument mark the lines that they may appear: then carve the grounds as deeply as you wish with different instruments, and sculp the figures or other things you please, according to your invention and skill." He tells how to make a knife handle with open work carvings, through which a gold ground is visible: and extremely handsome would such a knife be when completed, according to Theophilus' directions. He also tells how to redden ivory. "There is likewise an herb called 'rubrica,' the root of which is long, slender, and of a red colour; this being dug up is dried in the sun and is pounded in a mortar with the pestle, and so being scraped into a pot, and a lye poured over it, is then cooked. In this, when it has well boiled, the bone of the elephant or fish or stag, being placed, is made red." Mediaeval chessmen were made in ivory: very likely the need for a red stain was felt chiefly for such pieces. The celebrated Consular Diptychs date from the fourth century onwards. It was the custom for Consuls to present to senators and other officials these little folding ivory tablets, and the adornment of Diptychs was one of the chief functions of the ivory worker. Some of them were quite ambitious in size; in the British Museum is a Diptych measuring over sixteen inches by five: the tusk from which this was made must have been almost unique in size. It is a Byzantine work, and has the figure of an angel carved upon it. Gregory the Great sent a gift of ivory to Theodolinda, Queen of the Lombards, in 600. This is decorated with three figures, and is a most interesting diptych. The earliest diptych, however, is of the year 406, known as the Diptych of Probus, on which may be seen a bas-relief portrait of Emperor Honorius. On the Diptych of Philoxenus is a Greek verse signifying, "I, Philoxenus, being Consul, offer this present to the wise Senate." An interesting diptych, sixteen inches by six, is inscribed, "Flavius Strategius Apius, illustrious man, count of the most fervent servants, and consul in ordinary." This consul was invested in 539; the work was made in Rome, but it is the property of the Cathedral of Orviedo in Spain, where it is regarded as a priceless treasure. Claudian, in the fourth century, alludes to diptychs, speaking of "huge tusks cut with steel into tablets and gleaming with gold, engraved with the illustrious name of the Consul, circulated among great and small, and the great wonder of the Indies, the elephant, wanders about in tuskless shame!" In Magaster, a city which according to Marco Polo, was governed by "four old men," they sold "vast quantities of elephants' teeth."