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all the while with a glass rod； when the mercury has entirely left the
gold； grind the remainder in a Wedgewood's mortar； with a little water；
and when dried it will be fit for use。 The subliming the mercury is；
however； a process injurious to the health。
171。 COLOUR HEIGHTENING COMPOSITIONS
For yellow gold； dissolve in water 6 ozs。 of saltpetre； 2 ozs。 of
copperas； 1 oz。 of white vitriol； and 1 oz。 of alum。 If wanted redder； add
a small portion of blue vitriol。
172。 FOR GREEN GOLD
Dissolve in water a mixture consisting of 1 1/2 oz。 of saltpetre； vitriol
and sal…ammoniac； 1 1/4 oz。 of each； and 1 oz。 verdigris。
173。 FOR RED GOLD
Take 1 1/2 oz。 of red ochre in fine powder； the same quantity of calcined
verdigris； 1/2 oz。 of calcined borax； and 4 oz。 of melted yellow wax； the
verdigris must be calcined； or else； by the heat applied in melting the
wax； the vinegar becomes so concentrated as to corrode the surface； and
make it appear speckled。 These last three are colours for heightening
compositions。
174。 MOSAIC GOLD
Mosaic gold； or aurum mosaicum； is used for inferior articles。 It is
prepared in the following manner： 1 lb。 of tin is melted in a crucible；
and 1/2 lb。 of purified quicksilver added to it； when this mixture is
cold； it is reduced to powder； and ground with 1/2 lb。 of sal ammoniac；
and 7 ozs。 of flower of sulphur； till the whole is thoroughly mixed； they
are then calcined in a mattrass； and the sublimation of the other
ingredients leaves the tin converted into the aurum mosaicum； which is
found at the bottom of the glass； like a mass of bright flakey gold
powder。 Should any black or discoloured particles appear； they must be
removed。 The sal…ammoniac used here must be very white and clear； and the
mercury quite pure and unadulterated。 When a shade of deeper red is
required； it can easily be obtained by grinding a very small quantity of
red lead along with the above materials。
175。 DUTCH OR GERMAN GOLD
A gilding powder is sometimes made from Dutch gold； which is sold in books
at a very low price。 This is treated in the same way as the real gold leaf
in making the true gold powder。 It is necessary； when this inferior powder
is used； to cover the gilding with a coat of clear varnish； otherwise it
soon loses its metallic appearance。 The same remark applies； though to a
less degree； to Mosaic gilding。
176。 COPPER POWDER
This is prepared by dissolving filings or slips of copper with nitrous
acid in a receiver。 When the acid is saturated； the slips are to be
removed； or； if filings be employed； the solution is to be poured off from
what remains undissolved； small bars are then put in； which will
precipitate the copper from the saturated acid； in a powder of the
peculiar appearance and colour of copper； and the liquid being poured from
the powder； this is to be washed clean of the crystals by repeated
levigations。
177。 COMMON SIZE
The size used by painters for most sorts of common work is prepared by
boiling in water pieces of parchment； and of the skins of animals and fins
of fish； and evaporating the solution to a proper consistency。 It only
differs； however； from a solution of glue containing fewer foreign
ingredients； and in not being so strong。
178。 DR。 JOHN'S VARNISH FOR PLASTER OF PARIS CASTS
Take of white soap and white wax； each half an ounce； of water two pints；
boil them together for a short time in a clean vessel。 This varnish is to
be applied when cold； by means of a soft brush。 It does not sink in； it
readily dries； and its effect may be heightened by lightly using a silk
pocket handkerchief。
179。 GENERAL DIRECTIONS FOR BRONZING
This art is nothing but a species of painting； but far from being of the
most delicate kind。 The principal ingredients made use of in it are the
true gold powder； the German gold； the aurum mosaicum； and copper powder；
（all above described。） The choice of these powders is； of course； to be
determined by the degree of brilliancy you wish to obtain。 The powder is
mixed with strong gum water or isinglass； and laid on with a brush or
pencil； and when not so dry as to have still a certain clamminess； a piece
of soft leather wrapped round the finger； is dipped in the powder and
rubbed over the work； when the work has been all covered with the bronze；
it must be left to dry； and any loose powder then cleared away by a hair
pencil。
180。 BRONZING IN WOOD
This may be effected by a process somewhat differing from the above；
Prussian blue； patent yellow； raw amber； lamp…black； and pipe clay are
ground separately with water on a stone； and as much of them as will make
a good colour put into a small vessel three…fourths full of size。 This
mixture is found to succeed best on using about half as much more pipe
clay as of any of the other ingredients。 The wood being previously cleaned
and smoothed； and coated with a mixture of clean size and lamp…black；
receives a new coating with the above compound twice successively； having
allowed the first to dry。 Afterwards the bronze powder is to be laid on
with a pencil； and the whole burnished or cleaned anew； observing to
repair the parts which may be injured by this operation； next； the work
must be coated over with a thin lather of castile soap； which will take
off the glare of the burnishing； and afterwards be carefully rubbed with a
woollen cloth。 The superfluous powder may be rubbed off when dry。
181。 IN BRONZING IRON
The subject should be heated to a greater degree than the hand can bear；
and German gold； mixed with a small quantity of spirit of wine varnish；
spread over it with a pencil； should the iron be already polished； you
must heat it well and moisten it with a linen rag dipped in vinegar。
182。 BRONZING CASTS OF PLASTER OF PARIS
There is a method of bronzing casts of plaster of Paris analogous to that
which we have above given for bronzing wood； but it is not in much repute。
Such figures may be beautifully varnished by means of Dr。 John's varnish；
receipt No。178。 Casts of plaster of Paris may be made by receipt No。167。
183。 SHELL…LAC VARNISH
Dissolve in an iron kettle； one part of pearl…ash in about 8 parts of
water； add one part of shell…lac； and heat the whole to ebullition。 When
the lac is dissolved； cool the solution； and impregnate it with chlorine；
till the lac is all precipitated。 The precipitate is white； but its colour
deepens by washing and consolidation； dissolved in alcohol； lac bleached
by the above process yields a varnish which is as free from colour as any
copal varnish。
184。 CHLORINE FOR SHELL…LAC VARNISH
This may be formed by mixing intimately eight parts of common salt； and
three parts of the black oxide of manganese in powder； put this mixture
into a retort； then pour four parts of sulphuric acid； diluted with an
equal we