BURNING of Colours

BURNING of Colours, among painters. There are several colours that require burning; as,

First, lamp-black, which is a colour of so greasy a nature, that, except it is burnt, it will require a long time to dry. The method of burning, or rather drying, lamp-black, is as follows: Put it into a crucible over a clear fire, letting it remain till it be red hot, or so near it that there is no manner of smoke arises from it.

Secondly, Umber, which if it be intended for colour for a horse, or to be a shadow for gold, then burning fits it for both these purposes. In order to burn umber, you must put it into the naked fire, in large lumps, and not take it out till it is thoroughly red hot; if you have a mind to be more curious, put it into a crucible, and keep it over the fire till it be red hot.

Ivory also must be burnt to make black, thus: fill two crucibles with shavings of ivory, then clap their two mouths together, and bind them fast with an iron wire, and lute the joints close with clay, salt, and horse-dung, well beaten together; then set it over the fire, covering it all over with coals: let it remain in the fire, till you are sure that the matter inclosed is thoroughly red hot: then take it out of the fire; but do not open the crucibles till they are perfectly cold; for were they opened while hot, the matter would turn to ashes; and so it will be, if the joints are not luted close.