G E 
Sapphire.- —Take of the compofitioij for paftc ten 
pounds ; of zuffer three drams and one fcruple ; and of 
ihe calx CaJJii owe dram. Powder and fufe them. Or 
the fame may be done by mixing with the pade one- 
eighth of its weight of fmalt.' 
Topaz. —Take of tlie compofitions mentioned under 
Gi.ass in this volume, ten pounds, omitting the falt- 
petre ; and an equal quantity of the Gold-coloured hard 
Gi.ass. Powder and fufe them.—For Take 
of the compolition for blue palte already defenbed, ten 
pounds; of calcined bone, horn, or ivory, half a pound. 
Powder and fufe them.—For Opake white. Take of the 
compofition for parte ten pounds ; and one pound of cal¬ 
cined horn, ivory, or bone ; and proceed as before. 
Such is the method pf manufacturing factitious gems 
by the working jewellers in London.—The following is 
the mode adopted by the jew'ellers in France, as de- 
I'cribed bT M. Fontanieu, of the royal academy of 
fciences in Paris: 
Of the Bases or Pastes. —Altliough the differ¬ 
ent calces of lead are all adapted to produce the fame 
c.fect in vitrliic.ition, yet M. Fontanieu prefers, lead in 
fcales, and next to that minium, as being the mort con- 
rtantly pure. It is neceffary to lift throtigh a alk lieve 
the preparations of lead one v, iflies to make tife of in 
the vitrification, in order to leparate the groffer parts, 
as alfo the lead found in a metallic rtate when white 
lead in fcales is employed. The bale of factitious gems 
is calx of lead and rock-cryrtal, or any other Hone vitri- 
fiable by the calces already mentioned. Pure land. 
Hint, and the tranfparent pebbles of rivers, are ftib- 
rtances equally fit to make glafs : but as it is firll necef¬ 
fary to break the inalfes of cryrtal, rtones,. or pebbles, 
into fmaller parts ; fo by this operation particles of iron 
or copper are frequently introduced, and to thefe dull 
or greafy matters are alfo apt to adhere. The artirt 
therefore begins by putting the pounded cryrtal or peb¬ 
bles into a crucible, which he places in a degree of heat 
capable of making the mafs red hot ; he then pours it 
into a wooden bowl filled with very clear water; and 
fhaking the howl from time to time, the final 1 portions 
of coals furnilhed by the extraneous bodies fwim on the 
furface of the water, and the vitrifiable earth, with the 
iron, &c. rells on the bottom. Fie then decants the wa¬ 
ter; and having dried themafs, he pounds it, and fifts the 
powder through the fineft filk lieve : he then digerts the 
powder during four or five hours with marine acid, 
rtiaking the mixture every hour. After having decanted 
the marine acid from the vitrifiable earth, he wadies the 
latter until the water no longer reddens the tinCture of 
turnfol. The faid earth being dried, is parted through 
a filk fieve, and is then fit for ufe. Nitre, fait of tar¬ 
tar, and borax, are the three fpecies of falts that enter 
with quartz and thefeveral calces of lead into M. Fon- 
tanieu’s vitrifications. 
Mucli ot the fuccefs in the jeweller’s art depends on 
the accurate proportion of the fubrtances made ufe pf 
to lonn the cryrtal wliich ferves as a bale to the faCfi- 
rious gems. Alter having tried a great variety of re¬ 
ceipts, our autiior found they might be reduced to the 
lollowing :—i. Take two parts and a half of lead in 
fcales, one part and a half of rock-cryftal or prepared 
flints, half a part of nitre, as much borax, and a quarter 
part ot glafs ot arlenic. I'liefe being well pulverized 
and mixed together, are to be put into a Fielilan cruci¬ 
ble, and fubnutted to the fire. When the mixture is 
well melted, pour it into cold water : then melt it again 
a fecoud and a third time; taking care, after each melt- 
ing, to throw it into frelh cold water, and to feparate 
from it the lead that may be revived. The fame cru¬ 
cible Ihotild not be ufed a fecond time, becaufe the glafs 
ot lead is apt to penetrate it in fuch a manner as to run 
the ritk of loling the contents. One murt alfo be care¬ 
ful to cover the crucible well, to prevent any coals get¬ 
ting into it, which would Ipoil the compofition. 
M, 2J5 
2. Take two parts and a half of white cerufe, one 
part of prepared Hints, half a part of fait of tartar, and 
a quarter part of calcined borax : melt the mixture in 
a Heflian crucible, and then pour it into cold water; it 
is then to be melted again, and wafhed a fecond and a 
third time, the fame precautions being obferved as for 
the firrt bafe, 
3. Take two parts minium, one part rock cryrtal, half 
a part of nitre, and as mtich lalt of tartar : this mixture 
being melted, murt be treated as the former. 
4. Take three parts of calcined borax, one part of 
prepared rock-cryrtal, and one part of fait of tartar; 
thefe being well mixed and melted together, murt be 
poured into w'ann water: the water being decanted and 
the mafs dried, an equal quantity of minium murt be 
added to it; it is then to be melted and walhed feveral 
times as dircfled above. 
5. That parte called by Fontanieu Mayence bafe, and 
which he confiders as one of the fineft cryltalline com¬ 
pofitions hitherto known, is thus prepared : Take three 
parts of fixed alkali of tartar, one part of rock-cryftai 
or flint pulverized : the mixture to be well baked to¬ 
gether, and tiien left to cool. It is afterwards poured 
into a crucible of hot water to dilfolve the frit ; the fo- 
lution of the frit is then received into a ftone-ware pan, 
and aquafortis added gradually to the folution till it no 
longer effervefees : this water being decanted, the frit 
murt be w'afhed in warm w ater till it has no longer any 
tafte ; the frit is then dried, and mixed with one part 
and a half of fine cerufe or white lead in fcales ; and 
this mixture mull: be well levigated with a little dirtilled 
water. To one part and a half of this powder dried 
add an ounce of calcined borax ; let the whole be w'elF 
mixed in a marble mortar, then melted and poured into 
cold water as the other bafes alre<idy deferibed. Theie 
fufions and lotions having been repeated, and the mix¬ 
ture dried and powdered, a twelfth pc.rt of nitre murt 
be added to it, and tlien melted for the laft time ; after 
which a very fine cryrtal will be found in the crucible. 
6. For a compofition for furnifliing very fine white 
parte : Take eight ounces of cerufe, three ounces of 
rock-cryftal pulverized, two ounces of borax finely 
powdered, and half a grain of manganefe ; having melt¬ 
ed and walhed this mixture in the manner directed above, 
it will produce a very fine white cryrtal parte. 
Of the Colours. —The calces of metals are the 
fubrtances ufttally employed to colour fairtitious gems ^ 
and on the preparation of thefe calces depends the vi- 
vidnefs of their colours. 
. From Gold. —To obtain the mineral purple known 
by the name of precipitate of Cajfmt, M. Fontanieu em¬ 
ploys the following different procelfes :—i. Dilfolve 
fome pure gold in aqua regia, prepared with three parts 
of precipitated nitrous acid and one part of marine acid ; 
and to harten the dilfolution, the matrafs lliould be 
placed in a fand bath. Into this folution pour a folu¬ 
tion of tin in aqua regia. The mixture becomes tur¬ 
bid, and the gold is precipitated with a portion of the 
tin, in the form of a reddilh powder ; which, after be¬ 
ing walhed and dried, is calleci precipitate of Callius. 
T he aqua regia employed to dilfolve the tin is compofed 
of five parts nitrous acid and one part of marine acid : 
to eight ounces of this aqua regia are added lixteen 
ounces of diltilled water. Some leaves of Malacca till, 
about the lize and thicknefs of a fixpence, are then put 
into this diluted aqua regia, till it will dilfolve no more 
of them : which operation requires twelve or fourteen 
days; though it might probably be haltened by beating 
the tin ftill tiiinner, and then roiling it into the form of 
a hollow cylinder, or turning it round into fpiral convo¬ 
lutions, and tluis expoling a greater extent of furface to 
the action of the menl^rtium. In order to prepare more 
readily the precipitate of Callius, M. Fontanieu puts 
into a large jug eight ounces of folution ot tin, to 
which he adds four pints of dilhlied water: he after- 
I wards 
