Seer. VIL On the Formation of Coloured Pastes. 
ONS s pay, 74 
~ . In our article on Gems, p. 128, we have already had 
occasion to consider the. of coloured pastes, or 
fictitious s. Wehave described the method of Fon- 
| tanieu of making a colourless base, and afterwards 
communicating to it any particular tint by metallic 
~~ oxides; but as we have followed that ingenious author 
only in so far as his iments relate to the imitation 
of precious. stones, such as the oriental topaz, the ame- 
thyst, the hyacinth, and the beryl, we here resume 
the subject, and give an account of his method of pro- 
_. dueing other colours. 
ethod of | 1. From Gold.—To obtain the purple colour known 
ining hy the name of precipitate of Cassius, M. Fontanieu 
eens the following process. 
_ Distil in a glass retort, placed in a bath of ashes, 
some gold dissolved in aqua regia, made with three 
parts of nitrous, and one muriatic acid ; when the 
acid is passed over, and the gold contained in the re- 
tort appears dry, leave the vessel to cool, then pour it 
into some new aqua regia, and proceed to — as mt 
fore. a he aqua regia twice upon the gold, 
and. distil it. After’ these four canons pa by 
little and little into the retort some oil of tartar per de- 
meen which will occasion a brisk effervescence ; 
Ww this ceases, distil the mixture till it becomes dry, 
and then put some warm water into the retort. Shake 
the whole, and put it into a cucurbit, when a precipi- 
tate is deposited, the colour of which is either brown 
or yellow. After having washed this precipitate, dry it. 
2, From Silver —The oxide of silver being vitrified, 
produces a yellowish-grey colour. This oxide enters 
only into the composition of the yellow artificial dia- 
mond and opal, Mr Fontanieu introduces it into the 
2 base in the form of horn silver (/una cornea). In or- 
der to prepare it, he dissolves the silver in nitrous acid, 
and afterwards pours into it a solution of sea salt: a 
white precipitate is obtained, which, being washed and 
dried, melts’easily in the fire, and is soon volatilized, 
5 ae: ag amy with vitrifiable maies : 
_ 3. From —The oxide of co imparts to 
white glass the finest green colour ; bat if this metal 
be not exactly in a state of oxidation, it produces a 
brownish-red colour. 
. 4, From Iron.—Though it is commonly believed that 
_ the oxides of iron communicate a very fine transparent 
* red colour to white glass, M. Fontanieu could only 
obtain from it a pale red, a little opaque. The oxide 
of iron he employed, was in the, proportion of the 
“20th part of the base. There are various ways of 
eparing the oxide of iron called crocus martis, 
general it is necessary that this metal be so far oxi- 
dated that the magnet ceases to attract it. Thus one 
may use the scales of iron found upon the bars of fur- 
" maces, which serve to distil aquafortis. By digesting 
filings of steel with distilled vinegar, then evaporating 
- and replacing the vinegar ten or twelve times upon 
these filings, and drying them alternately, an oxide of 
sf iron is obtained, which must be. sifted through a silk 
sieve, and then calcined, The oxide of iron, thus 
obtained by the vinegar, only introduced into the 
bases a green‘ colour inclining to yellow. By the 
following process, one of the finest red colours is ob- 
tained:—Let an ounce of iron-filings be dissolved in. 
nitrous acid, in a glass retort, and distilled over a sand-» 
bath to dryness, After haying replaced the acid or the 
dry oxide, and re-distilled it a second and a third time, 
it is then edulcorated with spirits of wine, and after- 
wards washed with distilled water. — ; 
GLASS, 
315 
5. From Cobalt,—The oxide of cobalt is made use of Coloured 
for introducing a blue colour into glass: but as this metal _ Paste. 
is rarely free from iron and bismuth, it is first necessary Method of 
to separate them from it. This is done by calcining obtaining 
the cobalt ore in order to disengage the arsenic ; and colours 
next distilling the oxide in a retort with sal ammoniac, from diffe- 
when the iron and the bismuth are found sublimed with "®t metals. 
this salt. The distillation must be repeated with the 
sal ammoniac till this salt is no longer coloured yellow. 
_The cobalt which remains in the cornute is then cal« 
cined in a potsherd, and becomes a very pure oxide, 
which being introduced into the base, in the proportion 
of a 900th part, gives it a very fine blue colour. 
_ 6. From Tin.—The oxide of tin, which is of a white 
colour, renders opaque the glass with which it is melt~ 
ed, and forms white enamel. For this purpose, calcine- 
the putty of tin; then wash and dry it, and sift it 
through a silk sieve. Take six pounds of the second 
base, (See Gems, p. 128.) the same quantity of the. 
calcined putty of tin, and 48 grains of manganese. 
7. From Antimony.—Antimony is only susceptible of 
vitrification in a certain state of oxidation, and then it 
produces a reddish hyacinth-coloured glass; but if the 
antimony be in a state of.absolute calx, such as the.dia- 
phoretic antimony, then it is no longer vitrifiable, and 
may be substituted for oxide of tin, to make white ena- 
m 
8. From Manganese.—Employed in a small quantity, 
this metallic substance renders the glass whiter ; a lar~ 
ger quantity produces a very fine violet colour, and a 
still tee dose renders the glass black and opaque. 
There are two ways of preparing manganese. The most 
simple consists in exposing it to a red heat, and then 
quenching it with distilled vinegar : it is then dried and 
powdered, in order to pass it through a silk sieve. The 
other method of preparing the manganese proper to fur- 
nish a red colour, is described by Blancourt, who calls it 
“ fusible manganese.” Take of manganese of Piedmont, 
one pound ; torrefy and pulverize it; then mix it witha 
pound of nitre, and calcine the mixture during 24 hours ; 
afterwards wash it repeatedly in warm water, till the wa« 
ter of the leys has no longer any taste ; dry the manga- 
nese, ‘and mix with it an equal weight of sal ammo- 
niac ; levigate this mixture on a slab of porphyry, with 
sulphuric acid, diluted with water to the strength of 
vinegar. Dry the mixture, and introduce it into a-cor- ‘ 
nute: distil by a graduated fire; and when the sal am- 
» moniac is sublimed, weigh it, and add to the mixture 
an equal quantity. Then distil and sublime as before, 
and repeat the operation six times, being careful at each 
time to mix the sal ammoniac and the manganese upon 
the porphyry with diluted sulphuric acid. 
Compositions —To make the white diamond, take the Composi- 
Mayence base. This base is very pure, and has no co- tions to imi- 
lour. It is similar to the beautiful white paste, so gene- tate the 
rally known by the appellation of Strass. on 
For the Yellow Diamond.—To an ounce of the fourth *°"** 
base, add, for colour, 24 grains of horn silver, or ten 
grains of glass of antimony. 
For the Sapphire.—To 24 ounces of the Mayence 
base, add two drachms 46 grains of the calx of cobalt. 
For the Oriental Ruby.—1. To 16 ounces of the May- 
ence base, add a mixture of 2 drachms 48 tno of the 
precipitate of Cassius, the same quantity of crocus mar-_ 
tis prepared in aquafortis, the same of golden sulphur of 
antimony and of fusible manganese, with the addition 
of two ounces of rock crystal: or, 2. To 20 ounces of 
the base made with flints, add half an ounce of fusible 
manganese, and two ounces of rock crystal. 
For the Balas Ruby.—1. To 16 ounces of the May-, 
