Encyclopaedia Britannica; or, A dictionary of arts and sciences, compiled upon a new plan … > Volume 2, C-L

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this was the manner by which they wrought their lights,
and heightnings, on all kinds of colour.
The hr ft thing to be done, in order to paint or ftain
glafs, in the modern way, is to defign, and even co¬
lour the whole fubjeft on paper. Then they chufe
fuch pieces of glafs as are clear, even, and fmooth,
and proper to receive the feveral parts, and prbceed to
diftribute the deiign itfelf, or papers it is drawn on,
into pieces fuitable to thofe of the glafs ; always taking
care that the glafles may join in the contours of the fi¬
gures, and the, folds-of the draperies; that the carna¬
tions, and other finer parts, may not be impaired by
the lead with which the pieces are to be joined toge¬
ther. Tire diftribution being made, they mark all the
glaffes as well as papers, that they may be known
again : which done, applying every* part of the defign
upon the glafs intended for it, they copyt or transfer,
the defign upon this glafs with the black colour diluted
in gum v/ater, by tracing and following all the lines
anc^ ftrokes as they appear through the glafs with the
point of a pencil.
When thefe ftrokes are ell dried, which will hap¬
pen in about two days, the work being only in black
and white, they give airtight wafti over with urine, gum
arabic, and a little black; and repeat it feverai times,
according as the {hades are deTired to be heightened,
with this precaution, never to apply a new wafh till
the former is fufficiently dried.
This done, the lights and rifings are given by rub¬
bing off the colour in thp refpedtive places with a
wooden point, or the handle of the pencil,.
As to the other colours above-mentioned, they are
ufed with gum water, much as in painting in miniature ;
taking care to apply them lightly, for fear of effacing,
the out-lines of the defign ; or even, for the greater fe-
curity, to apply them on thebtherfide; efpecially yellow,
which is very pernicious to the other colours, by blend¬
ing therewith. And here too, as in pieces of black
and white, particular regard muft always be had not
to lay colour on colour, or lay on a new lay, till fuch
time as the former are well dried.
It may be added, that the yellow is the only colour
that penetrltes through the glafs, and incorporates
therewith by the fire; the reft, and particularly the
blue, which is very difficult to ufe, remaining on the
furface, or at leaft entering very little. When the
painting of all thb pieces is finifhed, they are carried
to the furnace', or oven, to anneal, or bake the co¬
lours.
The furnace here ufed is fmall, built of brick,
from eighteen to thirty inches fquare. At fix inches
from the bottom is an aperture to put in the "fuel,
arid maintain the fire. Over this aperture is a
grate, made of three fquare bars of iron, which tra-
verfe the furnace, and divide it into two parts. Two
inches above this partition, is another little aperture,
through which they take out pieces to examine how the
coffion goes forward. On the grate is placed a fquare
earthen pan, fix or feven inches deep ; and five or fix
inches lefs every way than the perimeter of the fur-
V.OL. II. No. 56. 2
G L A
trace. On the one fide hereof is n little aperture,
through which to make trials, placed direffly oppofite
that of the furnaces deftined for the fame end. In
this pan, are the pieces of glafs to be placed, in the
following manner. Fii ft, the bottom of the pan is
covered with three ftiata, or layers, of quick lime
pulverifed ; thofe ftrata being feparated by two other s
of old broken glafs, the defign whereof is to fecurs
the painted glafs from the too intenfe heat of the fire.
This done, the glaffes are laid horizontally on the laft
or uppermoft layer of lime.
The firft row of glafs they cover over with a layer
of the fame powder, an inch deep ; and over this they
lay another .range of glaffes, and thus alternately till
the pan is quite full; taking care that the whole heap
always end with a layer of the lime powder.
The pan being thus prepared, they cover up the
furnace vith tiles, on a fquare table of earthen ware,
cloftly luted all round; only leaving five little aper¬
tures, one at each corner, and another in the middle,
to ferve as chimneys. Things thus difpofed, there re¬
mains nothing but to give the fire to the work. The
fire for the firft two hours muft be very moderate, and
muft be increafed in proportion as the co&ion advances,
for the fpace of ten or twelve hours; in which time
it is ufually compleated. At laft the fire, which at
firft was charcoal, is to be of dry wood, fo that the
flame covers the whole pan, and even iffues out at the
chimneys.
During the laft hours, they make effays, from time
to time, by taking out pieces laid for the purpofe
through the little aperture of the furnace, and pan, to
fee whether the yellow be perfeft, and the other co¬
lours in good order. When the annealing is thought
fufficient, they proceed with great hafte to extinguifh
the fire, which otherwife would foon burn the colours,
and break the glaffes.
Glass of lead. See Chemistry, p. 136.
Glass porcelain, the name given by many to a modern
invention of imitating the china-ware with glafs.
The method of making it, as given byMr Reamur,
who was the firft that carried the attempt to any de¬
gree of perfedlien, is as follows.
The glafs veffels to be converted into porcelain, are
to be put into large vcffels, fuch as the common fine
earthen difhes are baked in ; or into fufficiently large cru¬
cibles : the veffels are to be filled with a mixture of
fine white fand, and of fine gypfum; or plafter ftone,
burnt into what is called plafter of Paris ; and all the
interftices are to be filled up with the fame powder, fo
that the glafis v^ffels may no where touch either one
another, or the fides ofijthe veffels they are baked in.
The vcffel is to be then covered down, and luted,
and the fire does the reft of the work : for this is only
to be put into a common potter’s furnace, and when it
lias flood there the ufual time of halting the other vef¬
fels, it is to be taken out, and the whole contents will
be found no longer glafs, hut converted into a wffiite
opake fubftance, which is a very elegant porcelain, and
has alraoft the properties of that of china.
( 721 )
Glass