fcce of the metal bare. While the mercury 
is evaporating the piece is to be, from time to 
time, taken from the fire, that it may be ex- 
amined ; that the amalgam may be spread 
more equally by means of a brush ; that any 
defective paits'of it may be again covered, 
and Ibat the heat may not be too suddenly 
applied to it. When the mercury is evapo- 
I rated, which is known by the surface be- 
I coming entirely of a dull-yellow colour, the 
I metal must then undergo other operations, 
I by which the tine gold-colour is given to it. 
’ First, the gilded piece of metal is rubbed 
|] with a scratch-brush (which is a brush com- 
j posed of brass wire) till its surface is made 
I smooth ; then it is covered over with a coinposi- 
I lion called gilding-wax, and is again exposed to 
the lire till the wax is burnt off. This wax is 
j composed of bee’s-wax, frequently mixed with 
I some of the following substances : red ochre, 
| verdigris, copper scales, alum, vitriol, bo- 
rax ; "but, according to Dr. Lewis, the saline 
j substances are sufficient, without any wax. 
By this operation the colour of the gilding 
k heightened; and the eifect seems to be 
j produced by a perfect dissipation of some 
mercury remaining after the former opera- 
1 tion. 
'Flie gilt surface is then covered over with a 
1 saline composition, consisting of nitre, alum, 
j or vitriolic salt, ground together, and mixed 
up into a paste with water or urine. The 
piece of metal thus covered is exposed to a 
certain degree of heat, and then quench- 
ed in water. By this method its colour is 
further improved, and brought nearer to 
that of gold. This effect seems to be pro- 
duced by the acid of the nitre (which is dis- 
engaged’by the sulphuric acid of the alum, 
during the exposure to heat) acting upon any 
J particles of copper which may happen to lit; 
upon the gilded surface. 
Lastly. Some artists think that they give 
an additional lustre to their gilt: work, by dip- 
; ping it in a liquor prepared by boiling some 
I yellow materials, as sulphur, orpiment, or 
1 turmeric. The only advantage of this opera- 
tion is, that part of the yellow matter remains 
1 in some of the hollows of the carved work, in 
w hich the gilding is apt to be more imper- 
1 feet, and to which it gives a rich and solid 
appearance. 
It may here be noticed, that the use of the 
1 aquafortis or nitric acid, mentioned in the 
j beginning of the process, is not, as is gene- 
| rally supposed, contined merely to cleansing 
: the surface of the metal to be gilt from rust 
| or tarnish; but it also' greatly facilitates the 
application of the amalgam to the surface of 
that metal, probably in the following man- - 
] ner: It lirst dissolve's part of the mercury of 
the amalgam; and when the solution is ap- 
plied to the copper, tiiis latter metal, having a 
j stronger disposition to unite' with the nitrous 
acid than the mercury has, precipitates the 
; mercurv upon its surface, in the same manner 
j as a polished piece of iron precipitates upon 
| its surface copper from a solution^ of blue vi- 
i triol. When the metal to be gilt is thus co- 
vered with a thin coat of precipitated mer- 
[ cury, it readily receives the amalgam. 
On the subject of gilding by amalgama- 
1 tion, Dr. Lewis has the following remarks : 
j “ There are two principal inconveniences in 
this business ; one, that the workmen are ex- 
i posed to the fumes of the mercury, and ge- 
I, nerallv, sooner or later, have their health 
f Von. I. 
GILDING. 
greatly impaired by them; the other, the loss 
of the 'mercury ; for though part of it is said 
to be detained in the cavities made in the 
chimneys for that purpose, yet the greatest 
part of’ it is lust. From some trials 1 have 
made, it appeared that both these inconveni- 
ences, particularly the first and most consi- 
derable one, might be in a good measure 
avoided, by means of a furnace of a due con- 
struction.” 
If the communication of a furnace with its 
chimney, instead of being over the fire, is 
made under the grate, the ash-pit door, or 
other apertures beneath the grate, closed, 
and the mouth of the furnace left open, the 
current of air, w hich otherwise w ould have 
entered beneath, enters now at the top, and 
passing down through the grate to the chim- 
ney, carries with it completely both the va- 
pour of the fuel, and the fumes of such mat- 
ters as are placed upon it. I he back part of 
the furnace should be raised a little higher 
above the lire than the fore part, and an iron 
plate laid over it, that the air may enter only 
at the front, where the workman stands, who 
will he thus effectually secured from the 
fumes, and from being incommoded by the 
heat, and at the same time have full liberty 
of introducing, inspecting, and removing, the 
work. 
If such a furnace is made of strong forged 
(not milled) iron plate, it will be sufficiently 
durable. The upper end of the chimney 
may reach above a foot and a half higher than 
the level of the tire; over this is to be placed 
a larger tube, leaving an interval of an inch, 
or more, all round between it and the chim- 
ney, and reaching to the height ot ten or 
twelve feet; the higher the better. The ex- 
ternal air, passing up between the chimney and 
the outer pipe, prevents the latter from being 
much heated, so that the mercurial fumes 
will condense against its sides into running 
quicksilver, which falling down to the bot- 
tom, is there caught in a hollow rim, formed 
by turning inwards a portion of the lower 
part, and conveyed by a pipe at one side 
into a proper receiver. 
Gilding iron or steel. In gilding iron or 
steel by means of an amalgam, as the metal 
has no’ affinity for the mercury, an agent 
must he employed to dispose the surface to 
receive the gildingl 'For this purpose a solu- 
tion of mercury in nitrous acid (aquafortis), 
or what the w orkmen call quicksilver-water, 
is applied to the parts intended to be gilded; 
the acid, by a stronger affinity, seizes on a 
portion of tiie iron, and deposits in the place 
of it a thin coating of mercury, which will not 
refuse an union afterwards with the gold 
amalgam that may be applied ; but by this 
process the surface of the metal is injured by 
the nitrous acid, and the union ot the mer- 
cury is very slight, so that a bright and du- 
rable gilding cannot be obtained. 
Another method. Sometimes a solution of 
blue vitriol is applied, with a camel’s-hair 
pencil, to the parts of the steel intended to 
be gilt. By a chemical action, exactly similar 
to what we have described as taking place 
when a solution of nitrate of mercury is em- 
ployed, a thin coating of copper is precipi- 
tated on the metal. Copper having an affi- 
nity for mercury, a kind of union may by this 
means be effected betw een the amalgam and 
the iron or steel, as the case may be. In 
whichever of these methods the amalgam is 
•ijj 
brought into union with fhe steel, the surface 
is injured by the action of the acid employed, 
and still a heat sufficient to volatilize the mer- 
cury must be afterw ards used. 
Gilding of iron h>j heat. When the sur- 
face is polished bright, it must be heated till 
it becomes blue. Gold leaf is then applied 
to its surface, and burnished down. It is then 
heated again, and another layer of gold bur- 
nished on it. In this manner three or four 
coats are given, according to the strength o,f 
the gilding intended. This is a more labo- 
rious process than the two last, but it is not 
attended with so much risk. 
An improved process for gilding iron or 
steel. 'I bis process, which is less known 
among artists than it deserves to be, may 
prove useful to those who have occasion to 
gild iron or steel. The first part of the pro- 
cess consists in pouring oFer a solution of 
gold in nitro-muriatic acid (aqua regia) about 
twice as much ether, which must be done 
with caution, and in a large vessel. These 
liquids must then be shaken together; as 
soon as the mixture is at rest, the ether wall 
he seen to separate itself from the nitro-mu- 
riatic acid, and to float on the surface. The 
nitro-muriatic acid becomes more transpa- 
rent, and the other darker than they were be- 
fore ; the reason of which is, that the ether 
lias taken the gold from the acid. The whole 
mixture is then to be poured into a glass fun- 
nel, the lower aperture of which is small; but 
this aperture must not be opened till the 
fluids have completely separated themselves 
from each other. It is then to be opened; 
by which means the liquid which has taken 
the lowest place by its greater gravity, viz. 
the nitro-muriatic acid, will run off; after 
which, the aperture is to be shut, and the 
funnel will then lie found to contain nothing 
but ether mixed with the gold, which is to be 
put into well-closed bottles, and preserved for 
use. In order to gild iron or steel, the metal 
must be first well polished with the finest eme- 
ry, or rather with the finest crocus marfis or 
colcotliar of vitriol, and common brandy. The 
auriferous ether is then to be applied with a 
small brush; the ether soon evaporates, and 
the gold remains on the surface of the metal. 
The metal may then be put into the fire, and 
afterwards polished. By means of this auri- 
ferous ether, all kinds of figures may be de- 
lineated on iron, by employing a pen, or line 
brush. It is in this manner, we believe, t hat 
the Sbhlinger sabre-blades are gilded. 
Instead of ether, the essential oils may lie 
used, such as oil of turpentine, or oil of la- 
vender, which will also take gold from its so- 
lution. 
Gilding of silver. Dissolve gold in 
the nitro-muriatic acid, and dip some linen 
rags in the solution ; then burn them, and 
carefully preserve the ashes, which will be 
very black, and heavier than common. When 
any thing is to be gilded, it must be previously 
well burnished ; a piece of cork is then to be 
dipped, first into a solution of salt in water, 
and afterwards into the black powder; and 
the piece, after being rubbed with it, must 
be burnished. This powder is frequently 
used for gilding delicate articles of silver. 
Gilding of brass and copper. Fine instru- 
ments of brass, in order that their surface 
may be kept longer clean, may be gilded in 
the following manner. 
