2682. To Preserve Vermilion

2682.    To Preserve Vermilion. It is a fact well known to artists that the splendidly bright color of vermilion (cinnabar, sulphide of mercury) has a tendency, especially if it has been mixed with white lead, to become blackish brown and very dark-colored in a comparatively short time. This tendency is altogether obviated if, previous to being mixed with oil, it is thoroughly and intimately mingled with flowers of sulphur, in the proportion of 1 part sulphur to 8 parts vermihon.

2683. Carthamine or Safflower Lake

2683.    Carthamine or Safflower Lake. "Wash safflower till the water comes off colorless; mix it with water holding 15 percent, of carbonate of soda in solution, so as to form a thick paste; leave it for several hours, then press out the red liquid, and nearly neutralize it with acetic acid. Next put cotton into it, and add successive small portions of acetic acid, so as to prevent the liquid becoming alkaline. In 24 hours take out the cotton, wash it, and digest it for half an hour in water holding 5 per cent, of crystallized carbonate of soda in solution. Immediately on removing the cotton, supersaturate the liquid with citric acid, and collect the precipitate, which must be repeatedly washed in cold water. For pink saucers the liquid is allowed to deposit in the saucers. Mixed with the scrapings of French chalk it constitutes rouge.

2684. Lakes

2684.      Lakes are also obtained from Brazil-wood and madder, by adding alum to a concentrated decoction of the former, or to a cold infusion of the latter (made by triturating the madder, inclosed in a bag, with the water), and afterwards sufficient subcarbonate of potash or soda to throw down the alumina in combination with the coloring matter. The precipitate is to be washed and dried. A little solution of tin added with the alum improves the color. Lakes may be obtained from most vegetable coloring matters by means of alum and an alkaline carbonate. Yellow lake is made from French or Persian berries, by boiling them in water with a little soda or potash, and adding alum to the strained liquor as long as a precipitate is thrown down. Or by boiling weld, or quercitron bark, in water, and adding alum and chalk in a pasty state.

2685. Rose Pink

2685. Rose Pink. Boil 6 pounds Brazil-wood and 2 pounds peach-wood in water, with 1/4 pound alum, and pour the strained decoction on 20 pounds sifted whitening.

2686. Sap Green

2686.    Sap Green. The expressed juice of buckthorn berries (and sometimes of other species of rhamnus, and also of privet berries) is allowed to settle, and the clear liquid evaporated to dryness. A little gum-arabic is sometimes added to the juice.

2687. Azure Blue, or Smalts

2687.  Azure Blue, or Smalts. The common qualities are made by fusing zaffre (roasted cobalt ore calcined with siliceous sand) with potash. A finer quality is obtained by precipitating a solution of sulphate of cobalt, by a solution of silicate of potash. Another cobalt blue is obtained by adding a solution of phosphate of soda to a solution of nitrate of cobalt, and mixing the precipitate, washed, but not dried, with 8 times its weight of fresh hydrated alumina. "When dry, heat it to a cherry red. It is permanent, but has little body. If ground too fine it loses its beautiful tint. It can be employed in fresco and sili-cious painting. It is not affected by sulphuretted hydrogen.