Properly prepared clay is
forced through the aperture of a die of the shape of the outside of the
tile, while a plug,--held by a support in the rear of the die,--projects
through the aperture, and gives the form to the bore of the tile. The
shape of the material of the tile, as it comes from the die, corresponds
to the open space, between the plug and the edge of the aperture. The clay
is forced out in a continuous pipe, which is cut to the desired length by
a wire, which is so thin as to pass through the mass without altering the
shape of the pipe. The short lengths of pipe are dried in the air as
thoroughly as they can be, and are then burned in a kiln, similar to that
used for pottery.
*Materials.*--The range of earths which may be used in the manufacture of
tiles is considerable, though clay is the basis of all of them. The best
is, probably, the clay which is almost invariably found at the bottom of
muck beds, as this is finer and more compact than that which is dug from
dry land, and requires but little preparation. There is, also, a peculiar
clay, found in some localities, which is almost like quick-sand in its
nature, and which is excellent for tile-making,--requiring no freezing, or
washing to prepare it for the machine. As a general rule, any clay which
will make _good_ bricks will make tiles. When first taken from the ground,
these clays are not usually adhesive, but become so on being moistened and
kneaded.
It is especially important that no limestone _pebbles_ be mixed with the
clay, as the burning would change these to quicklime, which, in slaking,
would destroy the tiles.
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