Engraving Precious Stones

When we examine the marvellous artistic productions, executed in cameo or intaglio, upon precious stones, we naturally think that the means employed must be numerous and complicated, but in reality the apparatus and the tools of the engraver are as simple as those of the lapidary. They consist of the lathe, and a series of little rods with heads of different shapes, all of which can be adjusted to the lathe.

The lathe, as will be seen from the appended figure, is a very simple affair. The axis, driven by the belt from the wheel, is pierced at the centre with an orifice, into which the tools for cutting the stone are firmly fixed by means of a screw. The engraver wets the extremity of the mounted rod with diamond-dust made into a paste with olive-oil, and as the wheel is in motion he applies the stone, properly prepared by the lapidary, and firmly cemented to a piece of reed, to the revolving tool. The diamond-dust enables the tool to cut into the stone with ease. As the design is frequently very elaborate and of the greatest delicacy, the tools are necessarily multiform.

Among the different varieties there are four most used. The first is hollow; it describes circles with the utmost facility, and serves, when required, to perforate hard stones. The second is a disk quite blunt at the edge. The third is a sharp-edged disk of very frequent use, serving as a saw. The fourth is a rod, terminated by a little sphere, and is very frequently used. Fig. 124 shows all the tools used by the engraver.

As precious stones suitable for engraving have always a considerable and sometimes a very high value, it is important to be able to make use of every portion of them. They are therefore sawn instead of being ground down, so that the portion removed may also be made use of. This operation may be performed in different ways. The most ancient and simple method consists in fixing the stone to the extremity of a support, and cutting it by the friction of a bow, strung with two iron wires twisted together, and impregnated with diamond-dust. This method, however, is both tedious and irregular, and hence instruments, infinitely more rapid and precise, have been substituted for the bow.

Fig. 125 represents the mill of the lapidary, with the polishing disk replaced by a steel disk with a cutting edge, against which the workman applies the stone with his left hand, while he sets the apparatus in motion with his right. The disk is sprinkled with diamond-dust, which the workman collects and keeps always supplied to the edges of the wheel. This work is usually performed by the lapidary, preparatory to the engraver's task; indeed, the stone is sometimes set by the jeweller before it is engraved, in which case it is embedded in cork. If it is merely shaped and not set, it is fastened upon a baton with lapidary's cement.

The tools and apparatus employed by the engraver are therefore very simple; but just as the sculptor, besides his chisel and block of marble, must have a certain amount of technical skill, and, above all, the artistic faculty, so is it with the engraver in hard stones.

To execute a high-class work of art on a stone of one colour is very difficult; but stones of different colours, and with the colours variously disposed, are those most commonly employed. Here the difficulty is enormously increased, for the artist, besides having to attend to the cutting, properly so called, has also to compose his design, and to observe that in working it out he takes the fullest advantage of the different colours of the stone.

We shall give one example to show the wonderful effects that are sometimes obtained by artists when working on stones of different colours. The design is that of a shepherd sitting on a rock with a staff in his hand. His face, hands, and legs are flesh colour; his coat has several holes in it through which his shirt appears; and the artist has taken advantage of a wood-coloured vein in the stone to represent his staff. Beside him is a tree with some green leaves on it, and having the trunk designed with the utmost fidelity.

Stones on which the design is raised above the general surface are called cameos; those having the design sunk below the surface are called intaglios.

The stones used for cameo-cutting are generally opaque or semi-transparent, such as the onyx, sardonyx, cornelian, agate, &c. They are suited for subjects of the most varied character.

Intaglios are very often executed in transparent stones, and the subjects treated in this manner are more limited in number. They are chiefly such as seals, devices, coats of arms, &c.

In modern times Rome has almost a monopoly of this class of production, exporting every year more than dollar 50,000 worth of them.

In the Paris Exhibition of 1867 several magnificent cameos by Girometti were exhibited. One of these was a grand composition, representing Ptolemy Philadelphus and Arsinoe, valued at dollar 6000, and executed on a superb oriental cornelian, which alone cost dollar 2000.