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Stained Glass
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·Back Cover
Detail of Medallion Window, Canterbury Cathedral, England
complete details for the making of stained glass windows.
    Concerning the process of making glass, it seems only necessary to state here that the leading characteristics of glass making remain today practically the same as when the monks of earliest times learned from the Greeks the art of glass composition.

Coloring Glass
    Theophilus gives exact directions for mixing the ingredients, composed of sand and silicate of powdered quartz, or flint, with soda or potash to make the sand melt under great heat.
    To this mixture was added various substances such as gold, copper, or manganese when colored glass was made. Since the earliest glass was designed to imitate precious stones, the various colors produced were called by their names, as ruby, sapphire, emerald, topaz, amethyst and pearl. While this early glass among the Greeks was used as much for mosaic wall pictures as for windows, its transparency was not deemed for first quality of excellence. The various foreign substances remaining in the materials used by the early glass makers often produced tints streaked with color, instead of clear, even ones such as we see in modern glass;
St. Edward the Confessor (St. Mary's Church, Ross, England)

St. Mary's Church,
Ross, England
but this very unevenness gave a quality to the glass rarely equaled by modern manufacturers.

Blowing Glass
    The next process in glass making was that of blowing the glass into a large bubble by means of a long hollow blow pipe that had been dipped into a pot of the molten glass. The workmen then blew the mass into a long cylindrical form, which was later cut and flattened out by moderate heat in the oven, to a flat piece ready to use. This is called "muff" glass.
    Another process was that of pouring the molten glass out on a flat surface and spinning it rapidly until cold into a large flat disk, called a "crown." This is known as "crown glass." All the early glass was made by these two processes. When the glass was to be cut to fit a definite shape the workman dipped his finger in water and ran it over a line where he proceeded to pass a hot iron. Lifting the piece he then bent it, and broke the glass