The Ottawa free trader. [volume] (Ottawa, Ill.) 1843-1916, 1888-02-25
CAMEO CUTTING.
DESCRIPTION OF A PROCESS GEN.
ERALlY LITTLE UNDERSTOOD.

onous Pebble of Brazil-siethods OF the
"Coiorer"-The Ensraver.
Canoes are of two kinds--those cut in
stone, or in petra dura, and those cut or
mollusk shells. The latter are found chiefly
on the African and Brazilian coast. They
show, as a rule, two layers-a pale coffee
color, or deep red and white. They are clas-
sified in the trade as the Bulls Mouth, the
Black Helmet, and the Queens Conch. The
first has red or sardonyx inner coat, the
second blackish ground and the third q
pink ground. The first are found mostly
at Madagascar and Ceylon, and the second
at Jamaica, Nassau and New Providence.
They are formed of three distinct layers Of
calcareous matter, and their peculiar struct-
ure, while 1t affords the greatest protection
to the animal, serves also to give the cutter
a secure foundation for his work.
Designs upon shell canoes, which are very
much softer than stone canoes, may be
effected by the process necessary in the treat
ment of the latter. Or, when the shell
yields readily, the cutter does not resort to
the engine, but, having drawn an outline
upon the prepared ground, cuts away from
it as the wood engraver does, with tools care
fully made for this particular industry. They
are files and gravers. The tool most used is
fiat on side and round on the other and
serves therefore either as gouge OF chisel.
OF Sicilian origin, the manufacture OF shell
canoes was carried from Italy to Paris; and
more than one half the output of the lapi-
daries goes to England and is thence sent to
the United States The shell cameo is, of
course, inferior, both in durability and ar
tistic quality, to the stone canoes, which
enable the engraver to give considerable
relief and remarkable fidelity to any design
which may be placed upon them.
The prize stones are those which show four
or five distinct layers of different colors.
Thus, for a heroic head, the face would be in
the Gghtest color, the helmet dark, the crest
a shade lighter, and the ground gray. Art
lists like to cut Medusa on stones having a
red layer, so as to use that shade on the
snakes The stones now in favor are those
showing layers of black and willie Of equal
breadth. Before a process Of coloring was
founder rebound, rather, for it is now
known to have been in use and lost in an
tiquity-German agates of two shades of gray
were much in demand, and many beautiful
designs We're engraved upon them. Very few
canoes seen in jewelers. cases confess to the
careless observer that their beautiful colors
and high polish are due more to chemistry
than to nature. The coloring process is very
curious.
The round chalcedonous pebble is the orig
inal stone cameo. In Brazil it is found in
river beds At Oberstein it is found under
the rocks that are the great ribs of the high
formation, and it lies freely also in the
ground like flint stones in chalk. From the
mills of Oberstein and Idar the lapidaries Of
the world are supplied When the pebble is
first tested the trier breaks off a small bit
and moistens the fragment with his tongue
He watches keenly the rapidity with which
the moisture is absorbed and whether the
absorption is in bands, and in one band more
rapidly than in another. Thus he con ect-
ures its capacity to receive color. The peb-
BILE may be nothing but what We call agate
but chemistry is going to make it onyx or
sardonyx. BY its sensitiveness to moisture
he rates its commercial value, and then it
goes not to the engraver but to the Sitting
mill, where its roughness is ground off, and
it is cut so as to bring the white stratum OF
layer uppermost. Then it is ground with
emery and polished with water and rotten
stone on pewter lap.
1t goes next to the colorer. He immcrses
it in honey and water, and for several weeks
it is kept in its bath at a temperature Just
below boiling When done it is transferred
to another tub, and covered with sulphuric
acid heated to $50 or 400 dogs After ten
hours it is finished 1t goes next into clean
water and is dried in an oven. After polish
ing it lies in oil, which removes the appear
ance of flaws and adds TO the brilliancy of
the polish Bran removes the oil The Sc
crets of the coloring have never been fully
understood, and the operation of the various
influences is uncertain 1t is taken for
granted that the honey invades the pores and
il carbonized by the sulphuric acid. The de-
position of the carbon increases the color Of
each band which the honey has permeated
If the color of the stone is uniform through
out it is natural if it has been chemically
heightened or produced by sulphuric acid,
which makes the black ground, or nitric
acid which produces the carnelian ground,
the color will be found on examination
superficial and uneven. Only experts can
detect pure chalcedony from colored agates.
If a portrait is to be engraved upon the
stone, many artists prefer first to make the
model in wax and prove it i'll plaster, as the
engraver of old tested the design he intended
to put in enamel upon gold. The model
ing accepted, and the stone selected of the
size and strata desired, it is placed upon II
cork and leather handle. which holds it so
firmly that it will not be displaced in the
slightest degree by the action Of the engine.
Then the artists task actually begins The
slightest error of eye, the least inflrnity Of
hand, and the failure is complete. The en-
graver and etcher apply sharp instrument
to the ground, upon which they operate.
The cameo engraver applies the ground to a
sharp instrument, which does the cutting
and which, in Amsterdam, in the diamond
factories, is run by steam power.
The engine is a miniature lathe head. 1t
stands on a solid table before the engraver,
and it is confronted by rows of small iron
tools, some Of which look like little wheels
on the ends of iron stems; and most Of them
like dentists tools of half the common
length. A microscope would be necessary
to discover that the smallest of them ends in
a disc for some Of the discs are less than the
one hundredth part OF an inch in diameter.
These little wheels are the cutters on the
cameo ground. They receive touch Of oil
and diamond dust just before the operation
L. IL