MOSAIC. There arc several kinds of mosaic, but all of them consist in imbed ding fragments of different colored sub stances, usually glass or stones, in a ce ment, so as to produce the effect of a pic ture. The beautiful chapel of Saint Law rence in Florence, which contains the tombs of the Medici, has been greatly ad mired by artists, on account of the vast multitude of precious marbles, jaspers, agates, avanturines, malachites, Ae., ap plied in mosaic upon its walls. The de tailed discussion of this subject belongs to a treatise upon the fine arts.
The latest improvement in Mosaic art has been effected by Mr. Prosser, of Bir mingham, England, in 1840, who found that if the material of porcelain (a mixture of flint and fine clay) be reduced to a dry powder, and in that subjected to strong pressure between steel dyes, the powder is compressed into one fourth of its bulk, and is converted into a compact substance of great hardness and density ; much less porous, and much harder than common porcelain, uncompressed and baked in the furnace. This discovery was first ap
plied to the manufacture of buttons Mr. Prosser, and Mr. Blashileld applied it to the formation of tessera'. He obtained cubes thus formed, and by the application of these in any forms, as squares for ter sillation , triangles and hexagons, to imitate the opus Alexandrinum, polygons, and rhomboids, or of any color, and by enam elling the surface with the most brilliant tints and gold, very good substitutes for the ancient glass mosaic were produced. They are cemented together in apattern form on a table previously, and when hard may be laid down on the required spot.