GLASS. 
v-c every day fee effeclcd in tlic cafe of prints affixed to 
witiiont any of the paper remaining, and alfo of 
copper-plate einbellifliments upon porcelain and queen's 
ware, we doubt not that the piihirc, while frefh, may, 
by well-managed preffure, be transferred from the paper 
to an even plate of ground glafs coated with a proper 
gluten, whifh flirdl not materially olfufeate its tranfpa- 
rency ; and experiment imifi; determine wlicther the pa¬ 
per may afterwaid be gently drawn or peeled off, or 
imifl: be burned away or dellroycd by a corrofive li¬ 
quid, if any fucJi can be found which will not injure 
the colours. 
Suppofe, then, the operation of removing the paper 
be fatisfaclorily performed ; proceed we now to fecure 
the indelibilii.y of the piclure. Let a fquare plate of 
call-iron, an infh or two in thicknefs, and as level and 
finooth as pollible, be furniffied on every fide wdth a 
metal ledge riling an inch or more in Jieight, which 
ought to be in two feparate pieces, the one permanently 
faltened to tlie plate, the other capable of being re- 
itioved at pleafurc, for the jmrpofe of laying in and 
taking out the glafs without violence. Vr'ithin tliat 
ledge let the glafs be fitted, clofely touching it on every 
fide, and lying with the painted furface uppermoll. Upon 
tliis lay another plate of gial's, fitted in the fame man¬ 
ner. Let, now, the metal frame, with the inclofed 
glaffes, be expoied to the aclion of fire until the glafs 
pff.ues, without being melted to abfolute fluidity, lhall 
neverthelels become fufficiently loft to coalefceinto one 
body under a Itrong prelTure. The body wliich conveys 
the prell'ure, and lies in immediate contail witlt the 
glafs, mull equally fit and completely fill the entire 
I'pace between tlie ledges, that there be no room for the 
loft glafs to fpread in any direction, fo as to dillort any 
of the lines of the picture. 
Thofe who have witneffed tlie procefs purfued in fuft- 
eniiig tortoile-lhell in the fire, and prefling it into the 
various fliapes of fnuff-boxes, etuis, &c. wiil not con¬ 
ceive much diSciilty in this ufe of the glafs. It may 
be managed by the aid of a machine I'omewhat liniilar 
to a common printing-prefs, with a Iblid metal 'plaiine, 
to fit and fill the frame, as above ; though much better 
contrivances may be found among the multifarious en¬ 
gines now employed for the purpofes of coiniiiy, and 
Itriking the heavy dies, than any we can pollibly luggeli. 
In whatever manner the two glalFes may be prelT'ed into, 
union, the united body may be afterward ground and 
polilhed; and, in proportion to the greater Imoothnels 
of tlie two comprelling bodies, the lels grinding and po- 
lifl’.ing will be afterward required. 
For painting on.gial's by means of mezzotinto prints, 
fee Back-Pain'i'ing, vol. ii. p. 603. 
For th.e purpofe of making fadlitious gems, a glafs 
balls is formed witli the addition of a large quantity of 
lead. The method of making it is this : Put a quantity 
of lead into a potter’s kiln, and keep it in a Itate of fu- 
lion with a moderate fire, till it is calcined to a grey 
powder; then fpread it in the kiln, and give it a greater 
beat, continually Itirring it to keep it from running into 
lumps ; continue this procefs till the powder becomes 
yellow ; then take it out, and lift it fine ; this is one of 
the calces of load. Take of this calx fifteen pounds, 
and cryrtalline frit twelve pounds ; mix them well toge¬ 
ther; put them into a pot, and fet them in the furnace 
for ten iicurs; calf the whole, when perfectly melted, 
into water; I’eparaie the lool'e lead from it, and return 
the metal into the pot; and after Handing in tufion twelve 
hours more, it will be fit to mix w ith any of the colour¬ 
ing matters adajited to the formation of factitious gems, 
or paftes for cou.nterfeit jewellery ; for which fee tlie 
article Gem, p. 294, of this volume. 
An ingenious method of painting, fpangling, and 
ilding, upon glafs, has been invented by Mr.'i arrant 
Bloomlbury-lquarc, Loiiaon ; and lie recommends the 
faCtice of it in the following words; “ My method oi 
Vol. V Hi. No. 529, 
(}')> 
painting, fpangling, and gilding, upon glafs, is wGi 
adapted for the ornamenting of carriage;, (urniture, rnu- 
lical inllrunicnts, or any other matters, vviiere Inch kind 
of ;^rtianient lhall be thought ncceffiry. It is entirely 
and was never before praCtifed by any perfon what- 
|bever. The painting imill be.performed on the back of 
the cryfial, or glafs, fo as, when linilhed, to appear on 
the front: the colour,; arc prepared in oil, or varnilh, 
as in other limihir work. 1 he parts of ornament wliich 
are to be of gold, mull be fitll iliadowcd on the giaf.i, 
and when quite dry, the gold-leaf 4 s to be laid on: lil- 
ver ornament may be done in the fame manner. For 
fpangling, with either metal, leave the parts to be 
fp.uiglcd till the lafl, then lliadow them, and, when dry, 
varnilh the parts with copal varnilli, and ftrew the 
fpanglcs on it while wet; when tiie I’paiigles are quite 
dry, varnilli tliem two or three times over. If the 
fpangling is to be white, ufe filver I'paiiglcs. If yel¬ 
low, ufe gold fpangles. If blue, glaze the parts to be 
fpangled with fine Pruliian blue, ground very fine in oil, 
or varnilli, and lay on filver fpangles. If green, glaze 
the parts with tranfparent green. If crinifon, ul'e the 
bell fine lake. If purple, ulc a mixture of Pruliian blue 
and fine lake. To make the painting apjiear more raifed, 
paint tlie ornaments, and leave the ground of the cryfial, 
or glafsj quite clear, and put another plate of gial's co¬ 
loured, behind the ghifs painted on.”—See further the 
article Gilding, in this volume. 
The prefent impimved metliod of polllliing and filver- 
ing plates of glafs for looking-glafl'es or mirrors, is per¬ 
formed as follows : When the plates of glafs have been 
cafi and annealed, they are pretty finooth on that fide 
which lay upon the mould in which they were call; on 
the other fide they are ufually rough and undulated ; 
yet both furfaces are to be ground perfectly even. Be. 
fore tliat operation is begun, they are examined, to fee 
whether they have not fonie defeCfis, fuch as deep cavi¬ 
ties, or cracks, which might hinder their being polilhed 
in their original fize. If any fuch defects are found, 
they are cut off by means of a diamond, in fuch a man¬ 
ner as to keep the plates as large as pollible ; for on 
their I'uperior fize depends their value. When the plates 
have undergone the requifite examination, the firlt ope¬ 
ration i.s, to make them thinner. For this purpofe they 
are placed on a very even table of Hone or wood, and 
fixed in a true horizontal polition, by means of a layer 
of plaficr. A \s orkman gets upon the plate, and treads 
it, fo as to force 'the plafter to fpread iti'elf evenly under 
the glafs. Other plates, eighteen inches or tw'o feet 
fquare, and alfo in the rough, are fixed, by means of 
plalter, upon flat pieces of wood of the fame dimenfioiis 
as the plates; taking care to place tlie I'lnoothell fide 
outwards, if the roughefi fide of the other plate is to be 
firlt polilhed, and vice verfa. Vv''hen the plalter is dry, 
thefe fmall plates are put upon the otliers ; and, upon 
the flat piece of wood to which they are fl.xed, is laid n 
Hone, for the purpofe of increaling the prellure. _ This 
Hone is let into a frame of wood, which has a kind of 
handle at each corner, and is made fall to the board con¬ 
taining the upper plate of glafs. Between the two glafs 
plates is thrown water,- mixed with fand, or with pow-- 
dered grit-fione, which fliould be rendered finer as the 
work advances. The workman, by moving the machine 
about by means of the handles, grinds the plates, by 
rubbing them againfi each other, fo that thofe plates 
which ferve to polilh the others become alfo polillied 
tlicmfelves ; but, being much I'maller in fize than the 
under ones, they are fooner ground finooth, and there¬ 
fore require to be changed from time to time. A kind 
of ruler, laid on the plates, ferves to difeover what parts 
are molt prominent, and require rubbing down. 
The lecond operation is to render the two plates even, 
after they have in the firlt place been made fmooth. 
For this purpofe two workmen, one at each end of the 
table, drive the machine from one to the otherj malj-ing 
7 P , 
