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CHAPTER XI.

OF BLUE, AND OF BUBNT YELLOW.

Blue was first manufactured at Alexandria, and after-wards by Yestorius at Puzzuoli. The method of makingit, and the nature of the ingredients, merit our attention.Sand is ground with flowers of sulphur, till the mixtureis as fine as flour, to which coarse filings of Cypriancopper are added, so as to make a paste when moistenedwith water; this is rolled into balls with the hand, anddried. The balls are then put into an earthen vessel,and that is placed in a furnace. Thus the copper andsand heating together by the intensity of the fire, im-part to each other their different qualities, and therebyacquire their blue colour. Burnt yellow, which is muchused in stuccos, is thus made. A lump of good yellowearth is heated red hot; it is then quenched in vinegar,by which it acquires a purple colour.

CHAPTER XII.

OF WHITE LEAD, VERDIGREASE, AND RED LEAD.

It will be proper to explain in what manner white leadis made, and also verdigrease, which we call seruca.The Rhodians place, in the bottoms of large vessels, alayer of twigs, over which they pour vinegar, and onthe twigs they lay masses of lead. The vessels arecovered, to prevent evaporation ; and when, after a cer-tain time, they are opened, the masses are found changedinto white lead. In the same way they make verdi-grease, which is called seruca, by means of plates of