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Powdered Color May:
In 1902, Auguste Verneuil, a French scientist, developed the process of making synthetic gem sapphires. The basic material is powdered corundum (A12O3), which gives carrot-shaped crystals called boules when fused. A small amount of iron and titanium imparts a blue color; cobalt, a green color; nickel and magnesium, a yellow color; and more than five percent of chromic oxide (CrzOs), a deep red color. The process has been called the flame-fusion method because an oxy-hydrogen flame is used. The oxygen carries the powder into the center of the flame. Crystal-lographic orientation may be controlled by using small seed crystals onto which the fused droplets fall.Apparently Niepce had no better results than Daguerre, but the immediate acceptance of daguerreotypes in monochrome outweighed the fact that the colors were not recorded. It was not long, however, before the lack was sensed, and daguerreotypists began to color their plates by hand. This was accomplished by carefully dusting on the surface dry powdered pigment.
The preparation and application of the patented materials used for the effect of rough plaster are simple. The material, in the form of a flour-like powder, is mixed with water and, in some cases, with oil. Powdered color may be added to the mixture, thus finishing the Wall in one operation. It is also possible to apply the white, colorless plaster—a thick pasty substance—alone, and when it is thoroughly dry, to add the desired color by means of a thin glaze, to give the effect of age. For applying the plaster, a trowel or brush is customarily used. For textural variations, all sorts of implements may be employed. These plasters, as a rule, will not crack, and if cracks do occur, they may be easily filled. Most commercial products for this form of Decoration are fast-drying, very hard, and permanent.
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