1. The artisan called the potter converts plastic materials into hard
and brittle vessels of various kinds, denominated, in general terms,
_earthen ware_.
2. Alumine is the basis of all clays, and is the only earth that
possesses the degree of plasticity which renders the operations of the
potter practicable. It is, however, never found or used in a pure
state, but in combination with other substances, particularly with
silex, lime, magnesia, and the oxyde of iron.
3. In the manufacture of vessels from argillaceous compounds, the
different degrees of beauty and costliness depend upon the quality of
the raw materials, and the labor and skill expended in the operation.
The various productions of the pottery may be classed under the
following denominations--common earthen ware, white earthen ware,
stone ware, and porcelain; but of each of these there are many
varieties.
4. _Common earthen ware._--This ware is made of a kind of clay very
generally diffused over the earth, and which is essentially the same
with that employed in making bricks. The potters are often supplied
with this material by the brickmakers, who select for them that which
is too tenacious, or _fat_, for their own purpose. All common clays
contain more or less of the oxyde of iron, which causes the wares made
of them to turn red in burning.
5. In preparing the clay for use, the potter adds to it, when
necessary, a portion of fine loam, in order to lessen its tenacity,
and to prevent the vessels to be made of it from cracking, while
undergoing the fire. When the materials have been mixed, and partially
incorporated with water, the mass is thrown into a tub, fixed in the
ground about one-half of its depth. In the centre of this tub, is
placed a shaft, in a perpendicular position, from which radiate, in a
horizontal direction, a number of knives or cutters.
6. This machine is put in motion by horse-power, and by it the clay is
repeatedly cut, and properly kneaded. The workman then cuts it into
thin slices with a small wire, and, having rejected all matters not
fit for his purpose, he further kneads it with his hands, and forms it
into lumps, corresponding in amount of matter with the different
vessels which he proposes to make.
7. For the best kinds of this ware, the same species of clay is used;
but then it is differently prepared. It is first dissolved in water;
and, when the coarser particles have settled to the bottom of the
vessel, the fluid suspending the rest is drawn off, and made to pass
through a sieve into a reservoir. After the particles of the material
have precipitated, the water is drawn off, and the residuum is thrown
upon a large flat pan or reservoir made of bricks, where the mass is
freed from its superfluous moisture by evaporation in the air, or by
means of artificial heat applied beneath. It is then laid by in a damp
place, for future use.
8. Before the clay, thus purified from extraneous and coarser
particles, is formed into vessels, it is beaten with a stout piece of
wood, until the mass has become of an equal consistence throughout,
and then repeatedly cut into two pieces with a wire, and slapped
together to expel the air. The former of these operations is called
_wedging_, and the latter, _slapping_.
9. _White and cream-colored wares_ are made of clays which contain so
little oxyde of iron, that it does not turn red in burning, but, on
the contrary, improves in whiteness in the furnace. There are several
species of white clay, found in many different localities, most of
which, however, are known under the denomination of _pipe-clay_; or
they are distinguished by the names of the places where they are
obtained.
10. In preparing these clays for use, they are reduced to a minute
division by machinery, and afterwards dissolved in water, and
otherwise treated in a manner similar to that used for the better
kinds of common wares, as described in the seventh and eighth
paragraphs. For the purpose of diminishing the shrinkage in the fire,
and with the view of increasing the whiteness of the ware, pulverized
flint-stone is added to the clay, in the proportion of about one part
of the former to five of the latter.
11. In reducing the silex to the requisite fineness, it is first
brought to a red heat; and, while in this state, it is thrown into
cold water, to diminish the cohesion of its parts. It is then pounded
by machinery, levigated with water in a mill, sifted, mashed, and
otherwise treated like the clay. The materials are mixed while in a
state of thin pulp.
12. The several operations performed by the potter, in converting the
clay thus prepared into different kinds of vessels, and in completing
the whole process of the manufacture of earthen ware, may be included
under the following divisions, viz., throwing, turning, pressing,
burning, painting and printing, and glazing. They are not, however,
all used in producing and finishing vessels of every shape and
quality.
13. _Throwing._--This operation is performed on a potter's wheel,
which consists of a round table, and some simple means to put it in
motion. The clay having been placed on the centre of this machine, the
workman communicates to the latter a rotary motion with his foot, and
gives the proposed form to the material with his hands, which have
been previously wet with water, to prevent them from sticking. This
method is used for all vessels and parts of vessels of a circular
form; and, in many cases, no other operation is necessary to give them
the requisite finish, so far as their conformation is concerned.
14. _Turning._--The vessels are cut from the thrower's wheel with a
small wire; and when, by the evaporation of moisture, they have become
firm enough to endure the operation, they are turned on a lathe. The
objects of this operation are to communicate to them a more exact
shape, and to render them more uniform in thickness. The potter's
wheel, with the addition of some contrivance to hold the pieces in a
proper position, is frequently used for turning. The coarser kinds of
common wares are never turned.
15. _Pressing._--Vessels, or parts of vessels, which are of an
irregular shape, and which cannot be formed on the wheel, are usually
made by a process called _pressing_. This kind of work is executed in
moulds made of plaster of Paris, and these are formed on models of
clay or wood, which have been made in the exact shape of the proposed
vessel. Sometimes individual specimens of the wares of one country or
pottery are used as models in another; in such cases, the expense of
the moulds is considerably diminished.
16. The moulds frequently consist of several parts, which fit
accurately together; for example, the mould for a pitcher is composed
of two pieces for the sides, and one for the bottom. In forming a
pitcher in such a mould, the material, which has been spread out to a
proper and uniform thickness, is laid upon the inside of each portion
of it, and the superfluous clay is trimmed off with a knife. The mould
is then closed, and thin strips of clay are laid over the seams; the
removal of the several pieces of the mould, completes the operation.
17. Handles, spouts, figures in relief, and other additions of this
nature, are separately made in moulds, and stuck on the vessel with
the same kind of materials, sometimes mingled with a small proportion
of plaster of Paris. These appendages are added after the vessels have
become partially solid in the air.
18. _Burning._--All vessels, even after they have been dried in the
atmosphere, are in a very frangible state; and, to render them
sufficiently firm for use, they are submitted to the process of
burning in a kiln. To preserve the ware from injury while enduring the
fire, the several pieces are enclosed in cylindrical boxes called
_saggers_, which are made of baked clay. These boxes are placed one
above another around the sides of the kiln, which is of a circular
form, and gradually tapering to the top.
19. In burning the coarser wares, every piece is not thus inclosed;
but, between every two saggers, a naked piece is placed. A moderate
fire is first raised, which is gradually increased, until the
contents of the kiln are brought to a red heat. The burning occupies
between twenty-four and forty-eight hours. All wares, except the
coarsest kinds, are twice, and sometimes thrice, burned; and, after
having been once submitted to the process, they are said to be in a
state of _biscuit_.
20. _Painting and printing._--When the vessels are to be ornamented
with colors, it is necessary, in most cases, that this part of the
work be done after the first burning. In China, and at the porcelain
manufactory in Philadelphia, the drawings are executed by hand with a
pencil. The same method is used in Europe in elaborate pieces of
workmanship. But, in the common figured wares, where but one color is
used, the designs are first engraved on metallic plates, and
impressions are taken from them on thin paper, by means of a
copperplate printing-press.
21. In transferring to vessels designs thus produced, the paper, while
in a damp state, is applied closely to the surface of the biscuit, and
rubbed on with a piece of flannel. The porosity of the earthen
material causes the immediate absorption of the coloring matter,
which, in all cases, is some metallic oxyde. For a blue color, the
oxyde of cobalt is used; and for a black, those of manganese and iron.
The paper is washed from the ware with a sponge.
22. _Glazing._--To prevent the penetration of fluids, and to improve
the appearance of the ware, a superficial vitreous coating is
necessary. This can be produced by the aid of various substances; but,
in a majority of cases, red lead is the basis of the mixture employed
for this purpose. Equal parts of ground flints and red lead are used
for the common cream-colored wares. These materials are mixed with,
and suspended in, water, and each piece is dipped in the liquid. The
moisture is soon absorbed by the clay, leaving the glazing particles
on the surface, which, in the burning that follows, is converted into
a uniform and durable vitreous coating.
23. _Stone ware._--The materials of this ware, as well as the mode of
preparing them, differ but little from those of the common and better
kinds of earthen wares. The clays, however, which contain but little
or no oxyde of iron are chosen, since this substance would cause the
ware to melt and warp, before a sufficient degree of heat could be
applied to give it the requisite hardness.
24. The glazing is formed by a vitrification of the surface of the
vessels, caused by the action of common salt thrown into the kiln,
when it has been raised to its greatest heat. This glazing is more
perfect than that on ordinary earthen wares, being insoluble by most
chemical agents. It is hardly necessary to remark that this method of
glazing precludes the use of saggers.
25. _Porcelain._--This ware exceeds every other kind in the delicacy
of its texture, and is peculiarly distinguished by a beautiful
semi-transparency, which is conspicuous when held against the light.
In China, it is made chiefly of two kinds of earth; one of which is
denominated _petuntze_, and the other _kaolin_; but both are varieties
of feldspar, found in the mountains, in different localities. They are
brought to the manufactories from a distance in the form of bricks;
the materials, as taken from the mines, having been reduced to an
impalpable powder in mortars, either by the labor of men or by
water-power.
26. These materials are combined in different proportions in the
manufacture, according to the quality of the proposed ware. In the
best kind, equal quantities are used; but for those of inferior
quality, a greater proportion of petuntze is employed. The
translucency so much admired in porcelain, or _tseki_, as the Chinese
call it, is owing to the petuntze, which, in burning, partially melts,
and envelops the infusible kaolin.
27. It is not known who was the inventor of porcelain, as the Chinese
annals are silent with regard to this point; nor do we know more of
the date at which the manufacture was commenced. It is certain,
however, that it must have been before the fifth century of the
Christian era. Since this ware has been known to Europeans, it has
been manufactured chiefly, and in the greatest perfection, in the
large and populous village of King-te-ching.
28. Porcelain was first brought to Europe from Japan and China, and
for a long time its materials and mode of manufacture remained a
secret, in spite of the efforts of the Jesuit missionaries, who
resided in those countries. At length, in 1712, Father Entrecolles
sent home to France, specimens of petuntze and kaolin, together with a
summary description of the process of the manufacture.
29. Shortly after this important event had transpired, it was
discovered that materials nearly of the same kind existed in abundance
in various parts of Europe. The manufacture of porcelain was,
therefore, soon commenced in several places; and it has since been
successfully carried on.
30. The porcelain wares of Europe are superior to those of the
Chinese, in the variety and elegance of their forms, as well as in the
beauty of the designs executed upon them; but, as some of the
processes successfully practised in China, remain still to be learned
by the Europeans, the Oriental porcelain has not yet been equalled in
the hardness, strength, and durability of its body, and in the
permanency of its glaze. The manufacturers of Saxony are said to have
been the most successful in their imitations in these respects.
31. The porcelain earths are found in various parts of the United
States, but particularly at Wilmington, in the state of Delaware.
Nevertheless, there is now but one porcelain manufactory in our
country, and this is yet in its infancy. The establishment is located
in Philadelphia, and it has been lately incorporated, with the
privilege of one hundred thousand dollars capital.
32. The principle of induration by heat, is the same in the
manufacture of earthen wares as in making bricks; and, as the latter
can be more easily dispensed with than the former in a primitive state
of society, it is but reasonable to suppose that earthen ware was
first invented; but the art of making bricks must have been practised
before the deluge, or the posterity of Noah would not have attempted
so soon as about one hundred years after that catastrophe, to build a
city and a tower of these materials. It is, therefore, evident, that
this art was of antediluvian origin; and it was probably one of the
earliest brought to any degree of perfection.
33. The art of the potter was practised more or less by every nation
of antiquity, and the degree of perfection to which it was carried in
every country corresponded with the state of the arts generally. The
Greeks were consequently very celebrated for their earthen wares. The
Etruscans have also been particularly noted for their manufacture of
the elegant vases which have been dug, in modern times, from the
depositories of the dead, in Lower Italy.
34. Until the commencement of the manufacture of porcelain in Europe,
this art continued in a very rude condition, although practised to a
considerable extent in many places. It was much improved in England
about the year 1720, by the addition of flints to the usual material;
and, between thirty and forty years after this, it was brought to
great perfection, in all its branches, chiefly through the scientific
exertions of the celebrated potter, Josiah Wedgewood.
[Illustration: GLASS BLOWER.]