Raftsman's journal. [volume] (Clearfield, Pa.) 1854-1948, 1858-12-01
CLAY AND ITS USES.

There are few substances more useful than
humble clay. 1t is emplo. ed to construct our
houses, in the form of bricks; and, under the
names of china and stone-ware. 1t assumes the
most varied and beautiful confgurations in YES
sells and articles employed in every household
When we reflect on the varied uses of clay, it
becomes an exalted material in our estimation,
because il is indispensable to the supply of SO
many wants. Yet although it has been employ
ed in the arts from time immemorial, its COM
position and qualities are not very generally
known. Clay is the product of several kinds
of rocks; its character being determined by
that from which it is derived. 1t is generally
found as sedImentary deposit, having been
disintegrated from rocks by the action OF wa
ter and the atmosphere. Common blue clay
is the product of slaty rocks, and is a mixture
of the oXyd of the metal aluminium and impal-
pable silica sand. 1t is the alumnous oxyd
which renders it unctuouS and plastic when
moist and capable, in that state, OF being
nodded into any form. The common clay used
in making bricks contains little oSyd OF
iron; this, when burned, imparts to them
their peculiar red color.
The manufacture of bricks IN our country
is carried on very extensively, involving the
investment of an immense aggregate capital,
and the employ ment of many thousand oper
atives. Within the past fifteen years, machines
have superseded hand-molding in brick max
ing, in large yards. All art icleS made of clay,
as burning in kiln, acquire the hardness of
the rocks of which their materials once form
ed part. Glars which contain an alkali and
iron, readily fuse at a high temperature, where
as neither alumina nor silica fuse, when un-
mixed with other substances. Burnt bricks
are simple cubes of clay submitted to pressure
in molds, and gradually dried, TO eyaporate the
moisture slowly; then they are exposed to
high heat in the burning process. AS clay
shrinks greatly when it is being dried and
burned, articles made of it must be fired very
carefully, or they will break to pieces or be-
come distorted in form. For this reason,
bricks, when nodded, arc first dried slowly in
the sun, before they are burned; during wet
weather, therefore, this business cannot be
carried on in our country in the common way.
Po,tcr's clay for stone-ware contains 43.5
parts of silica alumina, 1922; lime, 0.35; j.
ron, l !; water, Is. This clay is infusible in a
porcelain kiln; it only indurates in firing.
The glazed face of stone-ware is made by a
fusble composition put on the surface.
| Kaolin or porcelain ciays are generally found
ill beds seams among granitic rocks, from
! which they have been disintegrated. They
contain no irOD-teldsDar is their base. Most
of the stone-ware and fine porcelain which
come into our country from abroad are manu-
factured in Stafforshire, England, where Sl0,-
600, 900 worth of articles are made annually,
three-fourths of which exported-mostly
to America. English porcelain is cheaper, but
it is inferior to the French. As the gliding
and ornamenting OF china-ware greatly enhance
its value ,and, of course, increase the tariff dues
on il, much plain porcelain is now imported
into, and afterwards decorated in, Newly ork.
Fire clay is composed of alumina and silica; ;
and bricks made of it are very refractory
Those made for our household stoves cx-
horbitant in price, and generally inferior
in quality, they are liable to fuse in burning
what is called ssred ash'' anthracite coal, which
| contains little iron. a stove can be lined in
more durable manner with potter's clay than
with friedrich. at one-third the cost. 1t is ap-
| piled by plastering it on the metal, and allow
| ing it to dry slowly afterwards. This infor-
nation may be useful to many of our readers,
who can readily obtain uch clay.