In modern practice many white earths and some preparations of shells are used. Besides these, and white lead, there are also preparations of zinc, tin, and barytes, which are available in different departments of art. Of yellows, it was impossible for any one seeking to miss them, as they abound in most countries; and those of the most durable and best kinds, namely the ochres. The Attic and Gallic sils or ochres were pale, and were used for lights by Polygnotus and Micon; but there were many ochres found in Campania and in the hills not far from Rome, which were used both raw and burnt. The burning of ochres generally renders the colours more transparent and darker, so that some of the ochres assume a reddish hue, especially the Sienna earth. Common yellow ochre, when burnt, is the colour called light-red, admirable for flesh tints; and so indeed are many of the other red ochres, whether natural, or artificially coloured by fire. The ancients used the ochres of Scyros and Lydia for shadows. The dark earths from those countries resemble that called umber, produced in Umbria, the use of which might be unknown to the Greeks[238]. These different ochres continue even now to be used, and to them are added varieties of modern discovery, produced in England, Spain, and other countries. Orpiment, or the sulphuretted oxide of arsenic, was known as a pigment to the ancients. Its hue, approaching to gold, induced Caligula to attempt to extract gold from it; and it is said that he succeeded in procuring a small quantity from some brought from Syria. We are ignorant how the ancient painters applied it. Cennino says, it is neither good nor lasting in fresco or distemper; but that with glue or size, it may be used in other pictures. It is still used by painters, but is an uncertain colour[239].