S T O 
S T O 
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the purposes to which they are applied. It 
is necessary to mix the clay with some fine 
colourless sand, in order to prevent the ves- 
sels from contracting too much during the 
baking. 
Thus stone ware is composed of two mate- 
rials, pure clay and sand ; and the beauty of- 
the ware depends upon the purity and fine- 
ness of these two materials. What is called 
English stone ware is composed of tobacco- 
pipe clay and powdered flints ; delft ware is 
composed ot clay and tine sand ; and the 
coarsest wares of still more common clay and 
sand. 
The materials are ground very fine in a 
mill, then mixed together, and formed into a 
paste. The different vessels are coarsely 
moulded on the potter’s wheel, and allowed 
to dry till they can bear handling. After this 
they receive their destined form completely ; 
and" when they are sufficiently dry, they are 
covered with the requisite enamel, apd then 
put into the furnace and baked. 
Such, in general, is the method of manu- 
facturing stone ware. 1 he particular pro- 
cesses followed in the making ot porcelain are 
concealed by the manufacturers ; but the com- 
ponent parts are always analogous to those 
pointed out by Reaumur. The refractory in- 
gredient is a fine white clay, consisting essen- 
tially of alumina and silica, and the fusible 
ingredient is a mixture of siliceous sand and 
lime. 
It is necessary to glaze the surface of ves- 
sels, whether of stone w are or porcelain, both 
for the purpose of beauty and utility ; for 
the bodv of the vessel, or biscuit as it is 
called, would not be sufficiently compact to 
contain liquids. Now this glazing is of three 
kinds: 1. A vitrified metallic oxide. 2. An 
enamel. 3. A glass. M he first is applied to 
the coarsest vessels, the second to fine kinds 
of stone ware, the third to porcelain. 
The glazing of coarse vessels is formed by 
covering their surface while hot with a little 
litharge, whjph has the property of running 
into an opaque glass at a moderate heat when 
spread thin upon an earthen vessel. The co- 
' lour of this glazing is yellow or red. It is 
seldom perfect; hence these coarse vessels 
are frequently porous, and incapable ot resist- 
ing the action of corrosive substances. Com- 
mon salt is sometimes employed instead of 
lead. It facilitates the fusion of the surface 
of stone ware, and occasions a kind of vitrifi- 
cation. 
The glazing of fine vessels consists of 
white enamel. This is made as follows : 
one hundred parts of lead are melted with 
from 15 to 40 parts of tin, and the mixture 
oxidized completely, by exposing it to heat 
in an open vessel. One hundred parts of this 
oxide are mixed with 100 "parts of a line 
white sand composed of three parts silica and 
one part of talc, and with about 25 parts of 
common salt. This mixture is melted, then 
reduced to powder, and formed into a paste, 
which is spread thin over the porcelain vessel 
before it is baked. The excellency of a good 
enamel is, that it easily fuses into a kind of 
paste at the heat which is necessary for baking 
porcelain, and spreads equally on the vessel, 
forming a smooth glassy surface, without 
losing its opacity, or flowing completely into 
a glass. Its whiteness depends upon the pro- 
portion of the tin, its fusibility upon the 
lead. 
Porcelain is always covered with a glass, 
composed cf earthy ingredients, without any 
mixture of metallic oxides. Hence the high 
temperature necessary to fuse it, and the pro- 
perty which porcelain vessels have of resisting 
the action of the most corrosive substances 
precisely as common glass does. The sub- 
stance, commonly employed is felspar; a mi- 
neral of a fine white colour and foliated 
texture, which is found abundantly in the 
mountains. 
It is usual to paint both stone ware and por- 
celain of various colours. These paintings 
are often excellent, both in elegance of work- 
manship and in brilliancy of colours. The 
colours are given by means of metallic 
oxides, which are mixed up with other ingre- 
dients proper to constitute an enamel, and 
applied in the usual manner with a pencil. 
On this subject much light has been thrown 
by the experiments of YVedgewood ; and 
Brogniart has lately published a general ac- 
count of the processes at Sevres, of which he 
is director. 
The process differs a little according to 
the substance on which the colours are to be 
applied. When the vessels are covered with 
enamel, less flux is necessary, because the 
enamel melts at a low heat, and the colours 
readily incorporate with it ; but this renders 
them more dilute, and makes it often neces- 
sary to retouch them. The colours on ena- 
mel generally appear brilliant and soft, and 
are not liable to scale. The flux is either a 
glass of flint and lead, or borax mixed with 
flint glass. The colours are usually made 
into a paste by means of gum-water or vo- 
latile oils. Some of them are liable to alter- 
ation by the action of the lead on them. 
The colours applied upon hard porcelain, 
or porcelain glazed with felspar, are nearly 
the same as those applied on enamel, but 
more flux is necessary. They are not liable 
to dilution, as the felspar glaze does not melt 
at the heat requisite for fusing the colours 
and their flux. They are liable to scale off 
when repeatedly heated. 
Colours are sometimes applied over the 
whole surface of the porcelain ; the flux in 
that case is porcelain. But such colours are 
not numerous, because few oxides can stand 
the heat necessary for melting felspar without 
being altered or volatilized. 
1. Purple is given by means of the purple 
oxide of gold precipitated by the smallest 
possible quantity of rnuriat of tin. This oxide 
is mixed with a proper quantity of powdered 
glass, borax, and oxide of antimony, and ap- 
plied with a pencil. It cannot bear a strong 
heat without losing its colour. 
2. Red is given by oxide of iron. A mix- 
ture of two parts of suiphat of iron and one 
part of alum is calcined slowly, till if acquires 
a fine red colour when cold. This powder 
is mixed with the usual flux, and applied with 
a pencil. 
3. Yellow is given by the oxide of silver; 
or, by oxides of lead, antimony, and sand; 
green, by the oxide of copper ; blue, by the 
oxide of "cobalt; and violet, by the oxide of 
manganese. 
STOP, in music, a word applied by violin 
and violoncello performers to that pressure 
of the strings by which they are brought into 
contact with the finger-board, and by which 
r S T O 
the pitch of the note is determined. Hence 
a string, when so pressed, is said to be stopt. 
Stop of an organ. A collection of pipes 
similar in tone and quality, which run through 
the whole, or a great part, of the' compass of 
the instrument. In a great organ the stops 
are numerous and multifarious, commonly 
comprising the following : 
Open-diapason stop. A metallic stop which 
commands the whole scale of the organ, and 
which is called open in contradistinction to 
the stopt diapason, the pipes of which are 
closed at the top. 
Stopt- diapason stop. A stop, the pipes ot 
which are generally made of wood, and its 
base up to middle C always of wood. They 
are only half as long as those of the open dia- 
pason, and are stopped at the upper end with 
wooden stoppers or plugs, which render the 
tone more soft and mellow than that of the 
open diapason. 
Principal stop. A metallic stop originally 
distinguished by that name, because holding, 
in point of pitch, the middle station between 
the diapason and fifteenth, it forms the stand- 
ard for tuning The other stops. 
Twelfth stop. A metallic stop so denomi- 
nated from its being tuned twelve notes above 
the diapason. This stop, on account of its 
pitch, or tuning, can never properly be used 
alone. The open diapason, stopt diapason, 
principal, and fifteenth, are the best qualified 
to accommodate it to the ear. 
Fifteenth stop. A stop which derives its 
name from its pitch, or scale, being .fifteen 
notes higher than that of the diapason. This 
stop and the twelfth, mellowed and embodied 
by the two diapasons and principal, form a 
proper compound for accompanying choral 
parts in common choirs and parochial 
churches. 
Sesquialtera stop. A mixed stop running 
through the scale of the instrument, and con- 
sisting of three, four, and sometimes five 
ranks of pipes, tuned in thirds, fifths, ahd 
eighths, in small organs this stop is generally 
divided at middle C, when the lower part is 
called the sesquialtera, and the upper part 
the cornet. The whole of the stop lies above 
the fifteenth; the first rank being a seven- 
teenth, the second rank a nineteenth, ahd 
the third rank a* twenty-second, above the 
diapason. 
Mixture or furniture stop. A stop com- 
prising two or more ranks of pipes, shriller 
than those of the sesquialtera, and only cal- 
culated to be used together with that and 
other stops. The mixture is nearly the sapie 
as the sesquialtera, and greatly enriches the 
instrument. 
Trumpet stop* A reed Metallic stop,. so 
called because its tone is imitative of the 
trumpet. In large organs it generally ex- 
tends through the whole compass. The 
months of its pipes are not formed like those 
of the pipes of other stops, but resemble that 
of the real trumpet. At the bottom of each 
of the pipes of this stop, in a cavity called the 
socket, is fixed a brass reed, stopt at the 
lower end, and open in front; it is furnished 
with a tongue, or brass ring, which covers the 
opening, and which, when the wind is impelled 
into the pipe, is thereby put into a vibratory 
motion, which produces the imitative tone 
peculiar to this stop. The trumpet stop is 
the most powerful in the instrument, and im~ 
