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How It Is Made
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annealed in special leers, the plate is therefore laid on a big revolving table, and has the faces ground quite smooth and parallel to each other by flat rubbers pivoted on a beam spanning the table, and rotated automatically by friction against the glass. For the first grinding course sand is used; afterwards emery powder of graduated fineness; and lastly, rouge. The process is slow, as more than a third of the substance of the rough plate has to be removed, and plate-glass is therefore expensive. Despite difficulties of handling, plates 15 feet by 25 feet have been successfully rolled, annealed, ground, and polished.

PRESSING GLASS

    Tumblers, vases, and bowls, both plain and ornamental, are now very commonly made by compressing glass mechanically into moulds. A pressing-mould is constructed of several very accurately fitting parts which can be easily closed together or taken apart. To make a tumbler, a sufficient quantity of semi-solid glass is placed in the mould and squeezed by a plunger having the shape of the interior of the tumbler, till it rises and fills the space between the plunger and the mould. In this manner it is possible to manufacture elaborately patterned ware, the design