156 Mechanical and Technical Processes. Materials times. Madder does not appear until the Roman period. The red was a natural red ochre, and the white either chalk or gypsum. In early times the yellow was also ochre, but by the Eighteenth Dynasty orpiment was also used. Analyses to determine the paint vehicles have not been satisfactory. Beeswax was. certainly used, however, both for painting on and for coating finished work. Gesso, a mixture of whiting and glue, was freely used for painting on and for gild- ing, especially when the material to be coloured was plaster or wood. The usual bases for paint work were canvas, papyrus, plaster, pottery, mud, stone and wood. Scenes of brewing beer are numerous, especially in the Old Kingdom, where each process is sometimes accompanied by a brief description; while grape picking, treading, pressing and bottling the wine are depicted on tombs of the New Kingdom with great frequency and detail. In certain scenes the artists go as far as to depict the disastrous effects of over-indulgence. The details of brewing, involving the discussion of the chemical principles of fermentation in general, are rather beyond the scope of this chapter. It suffices to say that the ancient beer was made from barley, without any admixture of hops, the general process of manufacture being almost identical with that by which buza is now made in Egypt for the lower classes of the population. This to-day has an alcoholic content of some 7 per cent. < Mr. Lucas describes the preparation of modern buza in Cairo as follows: 1. A good quality wheat is taken, the dirt removed, and the wheat coarsely ground. 2. Three-quarters of the ground wheat is put into a large wooden basin or trough and kneaded with water into a dough, yeast being added. 3. The dough is made into thick loaves, which are lightly baked so as not to destroy the enzymes or kill the yeast.