Page:Proceedings of the Royal Society of London Vol 2.djvu/44

Rh by the name of minium to the Romans, who called our modern minium by the name of cerussa usta, in consequence of the mode of making it; which, on the authority of Pliny, is said to have been suggested by the accidental effects of a fire at the Piræus at Athens, by which ceruse was found converted into minium.

From the description which Pliny gives of an inferior sort of vermilion, formed by calcining certain stones found in veins of lead, the author is of opinion, that the mineral thus treated must have been a natural carbonate of lead, which becomes red when burned. Among the yellows examined by Sir Humphry Davy, were ochres of various tints, from being mixed with different quantities of chalk, and the yellow oxide of lead or massicot.

But though we have the evidence of Vitruvius that orpiment was known to the ancients, and of Pliny that a substance nearly allied to orpiment, termed Sandarach, was used by the Romans, the author has not been able to detect either of these sulphurets of arsenic in any of the ancient fresco paintings.

Among some rubbish collected in one of the chambers of the baths of Titus were several large lumps of a deep blue frit, which, upon being analysed, were found to consist of soda, silica, and oxide of copper. Upon examination of the different tints of blue observable in the paintings of the baths, as well as several blues in fragments of fresco painting from the ruins near the monument of Caius Cestius, and from excavations made at Pompeii, it appeared that they all consisted of the same blue frit, more or less diluted by admixture with carbonate of lime. There appears to the author every reason to believe this to be the colour described by Theophrastus, as discovered by an Egyptian king, and anciently manufactured at Alexandria. Vitruvius also speaks of the same colour under the name of cæruleum, made in his time at Puzzuoli, by heating together sand, flores nitri or natron, and filings of copper.

Though Pliny and Vitruvius speak of Indian blue, which appears to have been indigo, the author has not been able to discover any remains of it at this time; nor indeed of any other blue, excepting the frit before mentioned among the opake blues used by painters. But it is by no means uncommon to find among the ruins fragments of transparent blue glass, which are tinged with cobalt; and it would appear, from a passage in Theophrastus, that the Greeks considered cobalt as a species of, in consequence of its property of giving this blue colour.

Among the several shades of green observable in the baths of Livia, the baths of Titus, and elsewhere, the greater part are coloured by carbonate of copper; but one of them, which approached the olive, proved to be the common green earth of Verona. It seems not improbable that some of the greens which are now found in the state of carbonate of copper may have been originally laid on as acetates; for it appears from Theophrastus that the ancients were well acquainted with verdigris.

The only trace of any thing approaching to the ancient purple