Por′ce-lain.
Pottery — using the word as generic — made of a material which becomes vitrified and translucent by burning.
The term
burning is here used in preference to
baking, as that term is applicable to the first heating which converts the plastic clay into
biscuit.
The tests of porcelain, as contradistinguished from pottery in its specific sense, are the glassy fracture, its clear ringing sound when struck, the homogeneity of its outer and inner coat, its resistance to fire, water, and all acids but fluorhydric.
Porcelain is said to have been invented in
China the fourth century A. D. The name is derived from
porcellana (Portuguese), a fine white shell which was held to resemble the ware.
The potter's wheel is shown among the very earliest of the
Egyptian mural paintings.
In more than one instance the wheel is shown as being used in the molding of man from clay.
Porcelain, as well as other kinds of earthenware, is found in the
Egyptian tombs.
One green porcelain jar has hieroglyphics which define it as
Egyptian.
Other vases from
Thebes, Sakkarah, and Ghiseh are evidently
Chinese, and indicate the commercial acquaintance of the two peoples.
Two of these bottles were brought to
England by
Mr. Rawlinson, another was found in a previously unopened tomb, and others are in
European museums.
 |
|
Kneph the creative spirit of the Egyptians, making man on the potter's wheel from clay. |
They are of a rather inferior article of porcelain, and probably contained a drug, perfume, or dye when imported.
Many blue porcelain emblems and images are in the
Abbott Egyptian Collection, New York.
Many of the cups and vases discovered at
Thebes are elegant in form, proportion, and coloring, and are deeply vitrified in burning.
The porcelain of
China is believed to have been known to the Romans under the name of
murrhina vasa or
murrea vasa, although they had no idea of its mode of formation.
It was first introduced by Pompey, who dedicated cups of this kind to
Jupiter Capitolinus.
They are mentioned by Pliny, Martial, and others.
Pliny's guess at the way in which they are formed, “a substance formed by a moisture thickened in the earth by heat,” shows that they were not glass.
The latter was no novelty in the time of Pliny.
See glass.
Oriental porcelain was imported into
Europe by the Portuguese in the beginning of the sixteenth century; but this was not the first of the trade, though perhaps the first important venture in the way of porcelain merchandising.
Early in the fifteenth century, the
French king, Charles VII., had pieces in his collection: in 1487,
Lorenzo de Medici received several valuable porcelain vases from the Sultan of
Egypt.
The
Marchese Campori of
Modena cites a letter, written in 1567, referring to
Bernardo Carnigiani as the rediscoverer of the art of making porcelain.
This was more than a century before
Botticher, who was, however, an original (not first) discoverer.
The incident which directed
Botticher's attention to the subject was observing the contents of some crucibles in which some alchemical preparations had been heated.
This was noticed to resemble porcelain, which then was a curiosity and of great value.
The material which gave the peculiar character to the compound was ascertained to be a fine white clay, found on the road near Aue, which was excessively tenacious and clammy, but capable when dry of being reduced to a very fine powder, so that it had been used for hair-powder and went by the name of “Schnorr's white earth.”
It proved to be kaolin.
The French porcelain works were first established at
St. Cloud, in 1695, by Louis XIV.; at
Vincennes, 1740; removed to
Sevres, 1786.
The
Meissen,
Saxony, porcelain manufactory was established by Augustus II., Elector of
Saxony, in 1710.
Botticher invented the hard paste in 1706; the red ware like jasper, in 1711: white porcelain, in 1709; the perfect, white kind, in 1715.
He died in 1719.
Heroldt introduced gilding and painting in 1720; modeled groups, in 1731; porcelain made in
England, at Bow, in 1698.
Wedgwood ware was first patented, 1762.
Porcelain may be distinguished from the coarser earthenware as a pottery which is fine grained, compact, very hard, and somewhat translucid.
The latter quality is derived from its partial vitrification.
It has various colors.
Porcelain is divided into hard and tender.
The former is made in
Germany and in
Asia, and the latter is held to include the ironstone china and similar ware, so heavily manufactured in
England.
Kaolin is the principal ingredient, mixed with a peculiar mineral, as related elsewhere in this article in a report of the
French emissary who went to
China to discover the secret of the manufacture.
Its glaze is earthy and non-metallic.
Tender porcelain, on the contrary, consists of a vitreous frit, which is rendered opaque and less fusible by mixture with a calcareous or marshy clay.
Its glaze is an artificial glass composed of lead, silica, and an alkali.
This porcelain would melt at the heat which the other requires to burn it.
It is held to occupy a place between the hard porcelain and fine
stone ware.
It differs from the first in the friability of its paste, and its metallic glaze, and from the second in its transparency and stronger glaze.
The information gathered from the
French emissary who went to
China to spy out the process is published by the Royal Academy of
Paris, and is in substance as follows:—
There are three materials employed in forming the body of the ware, but all the three are never used at once.
The first is called
petuntse. It contains scattered shining particles, is fine grained, and is quarried from certain rocks.
It is prepared for use by first breaking it with hammers, then grinding it in mortars with iron pestles, and, lastly, it is washed over, taking only the white creamy matter which floats on the surface, which, after being dried and pressed into small cakes, is fit for use.
The second material is called
kaolin, and appears to be porcelain clay, namely, that which results from the decomposition of feldspar.
It is described as occurring in lumps in the clefts of mountains, covered with a reddish earth.
It is prepared for use exactly in the same manner as the
petuntse.
The third material is called
hoache. It is used instead of kaolin.
It has a smooth, soapy feel, and no doubt is either steatite or soapstone or agalmatolite.
It is prepared in the same manner as the preceding.
Porcelain made with this latter is much dearer than that made with kaolin.
It has an exceedingly fine grain, and is very light, but at the same time more fragile, and it is not easy to hit on the precise degree of heat that suits it. For the finest porcelain, four parts of hoache are added to one of petuntse.
Sometimes the body of the ware is made with kaolin: and then the article, when dry, is dipped in the hoache, brought to the consistency of cream; what adheres forms a thin layer, on which, when dry, are laid the colors and the glaze: and thus a porcelain finer than the common is obtained.
Hoache is also laid with a pencil, before glazing, on those parts of the common porcelain that are intended to have an ivory-white color.
For the fine kaolin porcelains, equal parts of that substance and of petuntse are employed: for the less fine, two parts of the former and three of the latter.
The ingredients being put together in due proportions, the mass is carefully tempered and kneaded by hand, and then the ware is wrought on the wheel, or for articles of irregular figure, which cannot be thus formed, is made by pressing the composition into molds and then uniting the several pieces by moist clay.
The piece, being formed, is very carefully dried, and is then covered with the glaze.
The white semi-transparent glaze is thus prepared: The whitest petuntse with green spots is pulverized and washed over, as already described: and to one hundred parts of the cream thus obtained is added one part of
che-kao (burnt alum or perhaps gypsum) previously pulverized.
A caustic potash lye is also
[
1766]
prepared, into which
che-kao is stirred, and the cream thus produced is collected.
The two creams are then mixed together in the proportion of ten measures of the former to one of the latter.
This composition it is which gives to porcelain glaze its whiteness and luster.
A brown glaze is made of common yellow clay washed over and brought to the consistence of cream and then mixed with the former glaze.
If the brown glaze is not to cover the whole of the surface, wet paper is laid on the reserved parts, which, after the glaze has been put on and has ceased to be fluid, is removed, and such blank parts are then painted in colors and covered with the common white glaze.
When the glaze is thoroughly dry, the ware is put into the furnace for the first time, whence it appears that the ware is never in the state of biscuit, — a circumstance in which the process materially differs from that adopted by the
European manufacturers, who put on the glaze after the first firing of the ware.
The flux used with those colors that are laid on over the glaze is made of quartz, calcined and pulverized, and then mixed with ceruse in the proportion of one of quartz to two of ceruse.
Red is given by
peroxide of iron, produced by calcining green vitriol: and a finer red is made of copper, but the particular process is kept secret.
The enamel colors are tempered to the proper consistence by a solution of glue, except those into the composition of which the ceruse enters; these latter are tempered only with water.
Petuntse and
kaolin (
Chinese names) are both derived from feldspar, which consists of silica, alumina, and potash.
Kaolin consists of decomposed feldspar, and petuntse is the powder of undecomposed feldspar.
The radical difference seems to be that by decomposition and exposure to the air the kaolin has acquired plasticity, has become a
clay. This being the case, it is easy to conceive the propriety of keeping the prepared clay in a condition to improve by exposure and age, before working it. Marco Polo, who was from 1274 to 1291 in the service of Kublai Khan, the Conqueror of
China, states that the heaps of porcelain clay were exposed in
China for thirty to forty years before using; so that men gathered the materials for their children and grandchildren.
The other material mentioned is hoache, and probably, as the Pere d'entrecolles remarks, is steatite; which is a compound of silica and magnesia.
We cannot go into all the particulars of the history of the art, nor describe the ingredients and compositions of the porcelains of
China,
Dresden,
Sevres,
Berlin,
Vienna, Bohemia, but must refer our readers to
Birch's “History of ancient pottery” (1858):
Marryat's “History of Pottery and Porcelain, Medieval and Modern” (1857); and Brogniart's “Arts Ceramiques.”
