Encyclopaedia Britannica > Volume 7, ETM-GOA

G L A
Glafs. will not readily mix with one another when put in-
—v—- to water, before they are cait upon the paper which
is to be coloured. There are feveral ways of making
thefe varioufly coloured glaffes, but the bell is the fol¬
lowing.
Dilfolve four ounces of fine leaf filver in a glafs vef-
fel in ftrong aquafortis; Hop up the veffel, and fet it
afide.—In another veffel, diffolve five ounces of quick-
filver in a pound of aquafortis, and fet this afide.—
In another gafs veffel, diffolve in a pound of aquafortis
three ounces of fine filver, firft calcined in this manner:
amalgamate the.filver with mercury, mix the amalga-
gam with twice its weight of common fait well puri¬
fied, put the mixture in an open fire in a crucible, that
the mercury may fly off, and the filver be left in form
of powder. Mix this powder with an equal quantity
of common fait well purified, and calcine this for fix
hours in a ftrong fire; when cold, walh off the fait by
repeated boilings in common water, and then put the
filver into the aquafortis. Set this folution alfo afide.
—In another veffel, diffolve in a pound of aquafortis
three ounces of fal ammoniac; pour off the folution, and
diffolve in it a quarter of an ounce of gold. Set this
alfo afide.—In another veffel, diffolve three ounces of
fal ammoniac in a pound of aquafortis ; then put into
the folution cinnabar, crocus martis, ultramarine, and
ferretto of Spain, of each half an ounce. Set this alfo
afide.—In another veffel, diffolve in a pound of aqua¬
fortis three ounces of fal ammoniac; then put into it
crocus martis made with vinegar, calcined tin, zaffer,
arid cinnabar, of each half an ounce ; let each of thefe
be powdered very fine, and put gently into the aqua¬
fortis. Set this alfo a'ide. — In another veffel, diffolve
three ounces of fal ammoniac in a pound of aquafortis,
and add to it brafs calcined with brimftoneybrafs thrice
calcined, manganefe, and fcales of iron which fall from
the fmith’s anvil, of each half an ounce ; let each be
well powdered, and put gently into the veffel. Then,
fet this alfo afide.— In another veffel, diffolve two oun¬
ces of fal ammoniac in a pound of aquafortis, and put
to it verdigreafe an ounce, red lead, crude antimony,
and the caput mortuum of vitriol, of each half an
ounce; put thefe well powdered leifurely into the vef¬
fel, and fet this alfo afide.—In another veffel, diffolve
two ounces of fal ammoniac in a pound of aquafortis,
and add orpiment, white arfenic, painters lake, of each,
half an ounce.
Keep the above nine veffels in a moderate heat for
15 days, ftiaking them well at times. After this pour
all the matters from thefe veffels into one large veffel,
well luted at its bottom; let this Hand fix days, ftiaking
it at times ; and then fet it in a very gentle heat, and
evaporate all the liquor, and there will remain a powder
of a purpliih green.
When this is to be_wrought, put into a pot very
clear metal, made of broken cryftalline and white glafs
that has been ufed ; for with the virghufrit,. or fuch
as has never been wrought, the chalcedony can never
be made, as the colours do not ftick to it, but are
confumed by the frit. To every pot of 20 pounds of
this metal put two or three ounces of this powder at
three feveral times ; incorporate the powder well with
the glafs; and let .it remain an hour between each time
of putting in the powders. After all are in, let it
Hand 24 hours ; then let the glafs.be well mixed, and
G L A
take an affay of it, which will be found of a yellowifli
blue ; return this many times into the furnace ; when
it begins to grow cold, it will fhow many waves of dif¬
ferent colours very beautifuly. Then take tartar eight
ounces, foot of the chimney two ounces, crocus mar¬
tis made with brimftone, half an ounce; let thefe be
well powdered and mixed, and put them by degrees
into the glafs at fix times, waiting a little while be¬
tween each putting in. When the whole is put in, let
the glafs boil and fettle for 24 hours ; then make a
little glafs body of it; which put in the furnace many
times, and fee if the glafs be enough, and whether it
have on the outfide veins of blue, green, red, yellow,
and other colours, and have, befide thefe veins, waves
like thofe of -the chalcedonies, jafpers, and oriental
agates, and if the body kept within looks as red as
fire.
When it is found to anfwer thus, it is perfeft, and
may be worked into toys and veffels, which will al¬
ways be beautifully variegated : thefe muft be well an¬
nealed, which adds much to the beauty of their veins.
Maffes of this may be polifhed at the lapidary’s wheel
as natural ftones, and appear very beautiful. If in
the working' the matter grow tranfparent, the work
muft be flopped, and more tartar, foot, and crocus mar¬
tis muft be put to it, which will give it again the ne-
ceffary body and opacity, without which it does not
fhow the colours well.
Chryfolite colour may be made of ten pounds of either
of the compofitions for hard glafs defcribed above, and
fix drams of calcined iron.
Red cornelian colour may bo. formed by adding one
pound of glafs of antimony, two ounces of the calci¬
ned vitriol called fcarlet ochre, and one dram of ,manga->
nefe or magnefia, to two pounds of either of the com-
politions for hard glafs. The glafs of antimony and
magnefia are firft fufed with the other glafs, and then
powdere'd-andground with the fcarlet ochre: the whole,
mixture is afterwards fufed with a gentle heat till all .
the ingredients are incorporated. A glafs refembling,
the white cornelian may be made of two pounds of ei¬
ther of the compofitions for hard glafs, and two drams-
of yellow ochre well waftred, and one ounce of calcined,
bones:. grind them together, and fufe them with a.
gentle heat..
Emerald colour.. See Green below.
Garnet colour. To give this colour to glafs, the work¬
men take the following method. They take equal
quantities of cryftal and rochetta frit, and to every
hundred weight of this mixture they add a pound of
manganele and an ounce of prepared zaffer: thefe are
to be powdered feparately, then mixed and added by
degrees to the frit while in the furnace. Great care;
is to be taken to mix the manganefe and zaffer very
perfectly ;. and when the matter has flood 24 hours in.
fufion, it may be worked.
Glafs of this kind may be made by adding one pound
of glafs of antimony, one dram of-manganefe, and the
fame quantity of the precipitate of gold by tin, to
two pounds, of, either of the compofitions for hard
glafs; or the precipitate of gold may be omitted, if
the quantities of th§ glafs of antimony and manganefe
be doubled.
Gold colour. This colour may be produced by ta¬
king ten pounds of either of the compofitions for hard.
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