Skins not valuable for art purposes were sent to the tanners to be converted into various kinds of leather. Tanning was highly developed, and the tanners turned out leathers which are to-day admired for their excellence. The tanners carried on their industries by chemical processes similar to those in use to-day. The scarcity of wood in Egypt led to the invention of various substitutes. One common substitute was a kind of _papier mâché_. This was manufactured out of linen, wood or vegetable pulp and various kinds of paste. When it was used for art work the molded forms were covered with lacquer or various kinds of stucco. Very beautiful objects were manufactured from these substances, which indicate that the artists possessed a wide practical knowledge of physical and chemical principles. Chemical knowledge was also well shown in their manufacture of glass. They excelled in this industry. All kinds of glass were made and decorated by staining and glazing. The glassmakers were able to imitate precious stones in glass and their glass-bead and enamel work has never been excelled. Some modern chemists express the opinion that glass making was carried to a greater degree of perfection in Egypt than any modern nation has attained. Egyptian porcelains were also finely executed. These were enameled, stained, and decorated in numerous ways. The colors, glazes, and art mediums employed by the artists in pottery and porcelain necessitated a wide chemical knowledge. Some of the pigments employed both in glass and porcelain ornamentation were made from metals. Their use required a knowledge of metallurgy. Metals like lead, nickel, manganese required fluxing and refining before they could be secured in a state sufficiently pure to be used as bases for colors. Not only did the artists know the value of many metallic oxides, but they understood how to secure the tints resulting from blending different oxides, and by acting upon metals with acids, just as they acted upon vegetable and metallic dyes with acids to get rare tones in linen dyeing. Mordants were employed in dyeing cloths and these were acted upon by acids and alkalies to produce various colors. We are dependent upon the relics which have been preserved for our knowledge of the chemical and physical learning of the Egyptians. No chemical books of theirs have come down to us, and inferences must be drawn from the results seen. In carrying out metallurgical operations, the Egyptians employed small blast furnaces and melting pots. Air was compressed by bellows and conducted into molten substances by pipes. The methods of metal working, melting, rolling, forging, soldering, annealing, and chasing were similar to common methods in use in modern times.