Up: Glassmaking
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
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