Polygnotus[1157] and Micon[1158] were the first to employ sil in painting, but that of Attica solely. The succeeding age used this last kind for strong lights only, and employed the Scyric and Lydian kinds for shadow painting. The Lydian sil used to be bought at Sardes; but at the present day we hear nothing of it. CHAP. 57. (13.)—CÆRULEUM. Cæruleum[1159] is a kind of sand. In former times there were three kinds of it; the Egyptian, which was the most esteemed of all; the Scythian, which is easily dissolved, and which produces four colours when pounded, one of a lighter blue and one of a darker blue, one of a thicker consistency and one comparatively thin;[1160] and the Cyprian, which is now preferred as a colour to the preceding. Since then, the kinds imported from Puteoli and Spain have been added to the list, this sand having of late been prepared there. Every kind,[1161] however, is submitted to a dyeing process, it being boiled with a plant[1162] used particularly for this purpose,[1163] and imbibing its juices. In other respects, the mode of preparing it is similar to that of chrysocolla. From cæruleum, too, is prepared the substance known as “lomentum,”[1164] it being washed and ground for the purpose. Lomentum is of a paler tint than cæruleum; the price of it is ten denarii per pound, and that of cæruleum but eight. Cæruleum is used upon a surface of clay, for upon lime it will not hold. A more recent invention is the Vestorian[1165] cæruleum, so called from the person who first manufactured it: it is prepared from the finer parts of Egyptian cæruleum, and the price of it is eleven denarii per pound. That of Puteoli is used in a similar manner,[1166] as also for windows:[1167] it is known as “cylon.” It is not so long since that indicum[1168] was first imported to Rome, the price being seventeen[1169] denarii per pound. Painters make use of it for incisures, or in other words, the division of shadows from light. There is also a lomentum of very inferior quality, known to us as “ground” lomentum, and valued at only five asses per pound. The mode of testing the genuineness of cæruleum, is to see whether it emits a flame, on being laid upon burning coals. One method of adulterating it is to boil dried violets in water, and then to strain the liquor through linen into Eretrian[1170] clay. CHAP. 58.—TWO REMEDIES DERIVED FROM CÆRULEUM. Cæruleum has the medicinal property of acting as a detergent upon ulcers. Hence it is, that it is used as an ingredient in plasters, as also in cauteries. As to sil, it is pounded with the greatest difficulty: viewed as a medicament, it is slightly mordent and astringent, and fills up the cavities left by ulcers. To make it the more serviceable, it is burnt in earthen vessels.