586 The Architectural Review and American Builders' Journal. [Alar., phire ; — red ochre ; gyp, or transparent, plaster-like talc ; and lit! arge of silver. All these colors are to be ground separately, upon a piece of copper a little hollowed, or in the bottom of a basin, with the water, in which gum- Arabic has been dissolved. To produce black, some scales of iron must be well ground, for two or three hours, or more, on the plate of copper, with one-third part of rocaille, and then be put into some vessel to be preserved. As soon as it becomes red in the fire, it is a good method to put into it a small quantity of soot, grinding this with it ; or copper burnt, mixed with the sparks of iron, is better, for the soot has no bod}'. For white, silicions earth must be heated red-hot in a crucible ; and then be poured out into common water to cal- cine it, and afterwards be reduced to powder. It must then be pounded in a marble mortar, with a pestle of the same, and be ground again upon a marble slab. One-fourth part of saltpetre is then mixed with it, and the whole is calcined. It is then pounded again and once more calcined in a quick fire, as before; and taken out of the crucible for preservation. When used, an equal quantity of plaster or g}*p must be added to it, which must be separately baked, and as much rocaille ; and the whole must be ground together on the plate of copper. To make yellow, silver must be put, in small pieces, to bake in the crucible, mixed with sulphur or saltpetre. When it is entirely heated, and taken out of the fire, it is to be emptied into a vessel of water. It is then to be pounded in a marble mortar, till it becomes fit to be ground on a porphyry stone, which it will be in the course of half a day, moist- ening it with water when it shall become dry. When ground it must be mixed with nine times as much red ochre, and the whole ground together for an hour. To obtain red, litharge of silver must be used ; scales of iron and gum-Arabic, each the weight of an escu, or French crown-piece; harderic, or iron ore, half an escu ; rocaille, three ounces and a half; sanguine — described by Felibien, as a red stone, of which crayons for drawings are made, therefore, probably red chalk — three ounces. The rocaille, the scales of iron, the litharge, and the harderic are to be ground together, for a full half hour, on the plate of capper. After this the sanguine is to be pounded very small in a thoroughly clean iron mortar, and then put aside. Next, the gum-arabic is to be ground in the same mortar, in order that it may extract what remains of the sanguine ; for it is necessary that the gum should be so dry, that it may easily be reduced to powder. When thus pounded, the gum and sanguine are to be mixed, and turned out upon the plate of copper, where the other drugs already are, and the whole ground together as quickly as possible ; for the sanguine wastes itself in grinding too much this time. Care must also be taken to keep the whole soft, and of the same consistence as other colors ; neither so moist that it will run, nor so hard that it cannot be tempered with the finger. It is, how- ever, much better that it should be a little hard than too soft. This compo- sition being placed upon the plate, must be put into a glass pointed at the bot- tom, which is of great importance, and it must then be poured into a little clear water. In the next place, this substance is to be tempered with the end of the finger, as much as possible, a small quantity of water being again added to it, and be made of the same consistence, or a little more liquid, as a stale yolk of egg. Thus tempered, it ought to be covered with a paper to secure it from the dust, and must be suffered to rest for three daj's and three nights, without being moved. After- wards, the purest part of the color, which swims at top, must be poured off into another vessel of glass, care, being taken not to shake any part. This
