y 
Obs 
‘Methods of ing, may be employed with success upon glass. But 
cutting 
Glass, - 
‘Brongniart’s 
after all, the painter must employ no colour without ma- 
king trial of it upon the slips of glass. The colours in 
general become more faint by longer continuance in the 
fire, because they sink deeper into the glass. But every 
preparation varies in this respect. All the colours are 
mixed up for the pencil with gum water in sufficient 
quantity to make them work properly. 
A number of very interesting experiments on the co- 
experiment lours obtained from metallic oxides, and fixed by means 
on the co- 
Jours from 
metallie ox- 
ides. 
Method of 
cutting 
glass. 
With the 
«diamond, 
of fusion either on porcelain or glass, have been made by 
M.Brongniart, director of the royal porcelain manufacto- 
ry at Sevres. In the preceding list, we have already 
given some of his results ; but in. our article PorceLain, 
which. that celebrated mineralogist has undertaken to 
_-furnish, for this .work,,our readers may expect the ful- 
Jest and most recent information on the subject. 
Src. IX. On the different Methods of Culling Glass. 
_. A plate of glass may be cut into any shape, either by 
the diamond, or by a bar of red hot iron. 
A late and intelligent writer (see Parkes’ Chemical 
Es<ays, vol. v. p. 208) remarks, that there is some- 
thing very mysterious respecting the action of the dia- 
mond in cutting glass: and he informs us, that if a sheet 
of glass, cut with a diamond, be examined before it is 
actually broken into its intended divisions, it. will be 
seen that it is entirely cut through except at the upper- 
most surface. If this statement be correct, the opera- 
tion of the diamond might well be pronounced myste- 
rious; but we can assure our readers, that we have had 
occasion to.examine the fissures or clefts produced by a 
diamond, and we have always found, that they com- 
mence on the upper side of the glass where the diamond 
is applied, and extend gradually downwards. This 
may be distinctly seen, by reflecting light from the se- 
‘ parated faces, and the progress of the fissure downwards 
will be marked by the change produced upon the reflect- 
ed light. We-conceive, therefore, that there is no myste- 
4y whatever in the action of the diamond. A piece of 
soft and smooth wood will cut a plate of coagulated isin- 
glass without any difficulty ; a piece of steel will, with 
the same ease, cut a plate of wood; and, in like man- 
ner, a diamond will cut a plate of glass with the same 
facility, because it is as much harder than the glass, as 
the wood is harder than the isinglass, or as the steel is 
harder than the wood. 
In order that the wood may cut the isinglass, or the 
‘steel the wood, tle cutting point must be smooth, other- 
wise the surfaces to be cut will be torn up or scratched, 
instead of being really divided. For the same reason, 
the diamond must have a smooth natural point, or so- 
lid angle ; for if apiece broken from a diamond is em- 
ployed, it will only scratch the glass. 
Mr Atwood, in a communication to Mr Parkes, in- 
forms us, that a good cutting diamond should be of a 
regular rhomboidal form, or have one regular smooth 
edge and rhomboidal point. The least deviation of the 
diamond from a particular position and inclination will 
prevent the cut from taking place. The workman, who 
is guided altogether by his ear, judges by the peculiar 
creaking of the glass ; and if he does not hear this par- 
ticular noise, he varies the position of the diamond till 
it occurs, and then draws it onwards. The diamond 
apparently wears down at the cutting point by long use, 
though it will last an ordinary glazier for many years. 
« When the cut is perfectly good,” says Mr Atwood, 
« it should be an internal fracture, unaccompanied with 
any scratch, or any visible impression on the surface 
GLASS. 
whatever ; for in proportion as any such.superficialin= Meth 
jury is pradnerd the mares wy Peas a 
ture is diminished. This fracture, therefore, which i 
called a cut, from its resemblance thereto in its 
as also in the similarity of its appearance to a r 
produced on any other substance by a sharp edged instru- 
ment, but which has closed again, (the expression bg ng 
further countenanced, by thesharp form of hms of the 
diamond which comes in contact with the glass,) is real 
ly no cut at all, nor does the diamond so much as erft 
the surface.” If this reasoning be just, it will follow, 
that a good diamond is not capable of making any, i 
pression upon the surface of a plate of glass over which 
itis drawn, and that it acts where it is not, and does not 
act where it is. It would require singular ingenuity to 
support such paradoxes. eaet 
t.Shaw, an ingenious watchmaker in Lei Sh: 
shire, being desirous of giving some assistance to a ree tent 
lation of his own, who was a glazier, and who, by a pa- ® 
ralytic affection, was unable to pursue his trade, invent- 
ed a method of String up a diamond, by which any 
person can cut as perfectly as the most experi- 
enced glazier. This ae — made about a y: 
ago, and its advantages have been secured by a patent. 
« By the use of one of these instruments,” says Mr 
Atwood, “ a person not at all accustomed to a diamond, 
may produce a perfect cut over a table of glass so un- 
even in its surface, that the most skilful wor , With 
a common glazier’s diamond, would not be able to pro- 
duce a cut of any kind upon it. This consists in giv- 
ing, the siamo Restor ry, and at oe hid time af 
ording it suc ide and support, as effect vent 
it from being affected by the unsteadiness of the band. 
or unevenness of surface ‘in respect of its inclination to 
the plane of the table; whereby the diamond, being well 
set or mounted in its carriage, becomes equally certain 
in the hands of every person.” Parkes’ Chemical Es. 
says, vol. y._ This patent diamond is represented in 
Plate CCLXXV. See the description of this Plate at 
the end of the volume. ‘ 
When a plate of glass is very thick, it cannot be yy 
easily cut by the diamond ; but the same effect may be cut 
produced by the proper application of a hot iron. The glassb 
part of the glass where the cut is to commence must be hot ir 
marked by a file, and a hot iron must be applied to the 
place, and held a little below the groove which the file _ 
lias made. In a few minutes the glass will give acrack, - 
and the iron must be instantly removed. The iron must _ 
be again applied a little below the termination of thi 
crack, sometimes one-tenth or two-tenths of an inc 
distant from it, and in the line in which the cut is to be 
made, and the crack will advance in the direction of the 
iron. By again applying the iron in a similar manner, 
the crack may be conducted in any required direction. — 
If the glass is to be cut in the form of a curve, then the 
hot iron must always be held very near the terminati 
of the crack, in order that it may advance by short steps 
The fissure is often most complete on the side of te j 
glass where the iron is enn and it is sometimes ad- 
visable to apply the iron to the opposite side, By this 
means, we have often cut plates~of glass four-tenths of 
an inch thick with the utmost accuracy, Se i‘ 
Glass may also be cut under water by a pair of scis- 7 
r 
oth # 
y 
sars, but in an imperfect manner. If the operation 
performed under a thick viscid fluid, the effect saa ‘ 
be still more complete, Neus st ie 
Szcr. X. . Physical Properties of Glass... 
There is perhaps no substance to which the progress 
