1833.] Miscellaneous. 213 
cles, such as figured jugs, ground flint is employed in place of sand. The com- 
position is brought by the addition of water, to the state of mortar, and is then 
tempered in the pug-mill. All round articles are made on the horizontal wheel ; 
and those of great size, 7. e. of a greater capacity than two gallons, are at first of 
extraordinary thickness below to support the upper part ; when they come off the 
wheel they are dried, and then put on the wheel again, and shaved down to a pro- 
per thickness. For oval, and other figures not circular, as pans for salting hams 
in, the clay is formed in a mould to the required shape. ‘The drying, especially of 
large articles, must be very carefully performed; and as, from custom, the tops or 
bottoms of jars and various other vessels made of this ware, are required to be of 
a deeper brown than the natural colour of the materials, they are dipped in a mix- 
ture of red-ochre and clay slip. When perfectly dry they are piled in the furnace, 
bits of well-sanded clay being put between each piece to prevent them from adher- 
ing. A slow fire is kept up for twelve to twenty-four hours, according to the 
thickness of the ware, capable of bringing it just to a low red heat. The fire is 
then to be raised till the flame and the ware are of the same colour, and is so to 
be continued for several hours. At this time the glaze is added, which is done 
by pouring down the holes in the top of the kiln, twenty or thirty in number, 
ladlesful of common salt. This, being volatilized by the intense heat of the inte- 
rior, attaches itself to the outer surface of the ware: here itis decomposed, the 
muriatic acid flying off, and the soda remaining behind in union with the earth, 
with which it forms a very thin, but, on the whole, a perfect glaze ; at least quite 
sufficient, with the compactness of the ware, to render it completely proof against 
the percolation, not only of water, but of the strongest acids. So perfect, indeed, 
is the texture of the best ware now made, that it has of late been very largely used 
in the construction of distillatory vessels for manufacturing chemists, instead of 
green glass, as being more durable and also cheaper. Pickling jars, and many 
other vessels in which acid substances for food or condiment are kept, as also 
those earthen vessels in which great strength is required, are best made of stone- 
ware. Vauxhall is the chief seat of this manufacture. There are now about 
eight houses engaged in this fabric, most of which are very actively employed, as 
the use of it is considerably on the increase.” 
In the porcelain of China, so justly celebrated for its beauty and excellence, the 
glaze is produced by a wash of clay of a kind more fusible than that of the body 
of the ware. 
Three materials are known to be employed in this manufacture. 1. Petuntse, which 
is quarried from certain rocks and contains shining particles : (mica ?) the lumps of 
this clay are broken up and ground in iron mortars, then lixiviated, and the creamy 
matter only used. Mr. Aikin supposes it to be a compact felspar; perhaps it may 
be a decomposing granite, from which the felspar is thus coarsely separated. 2. 
Kaolin, true porcelain clay, or decomposed felspar found in lumps in the clefts of 
mountains, covered with a reddish earth (just as it occurs in India). It is prepared 
for use like the petuntse. 3. Hoaché, which has a soapy feel, and is either steatite 
soapstone, or agalinatolite. It is also prepared in the same way, but is whiter, more 
transparent, and is used only for the more expensive wares. 
For the finest porcelain, four parts of hoaché are added to one of petuntse. Some- 
times the body is made of kaolin, dipped when dry into the cream of hoaché, which 
gives a white coat. Hoaché is also laid on with a pencil on the parts intended to 
have an ivory-white colour, 
