1200, and called a colouring tool. The front edge of this tool is used to cut the first line to the required depth, and the second line is at the same time marked out by the back edge; at the next process the second line is cut to the full depth, while the third line is marked in the same manner and so on; the lines being cut in succession from right to left, in order that the operator may be enabled to watch the progress of the tool throughout, and the stone is held in an inclined position, to cause the greater penetration of the front edge of the tool.
The colour lines are sometimes cut before the bearings are sunk, but at other times they are left until nearly all the other details have been completed, the latter course is adopted in order to avoid the risk of injuring the colour lines should the stone happen to slip in cutting the bearings, but the difficulty of cutting the lines, straight and equi-distant, is increased, owing to the want of continuity in the surface, and the tool is liable to cut deeper at the edges of the sunken portions. On this account in the best works the colour lines are usually cut before the bearings, but greatly increased care is then required in cutting the bearings.
When the engraving is quite finished, the flat surface of the stone is finally repolished with rottenstone and water, applied on a pewter lap, exactly after the manner described in the chapter on lapidary work.
During the entire process, the seal engraver watches the progress of the work through a lens of from 1 to 2 inches focus, which is mounted upon an adjustable stand, like that used by watchmakers, and placed immediately over the tool, and the work is occasionally brushed to allow of its inspection; but the seal engraver depends also very much upon the sense of feeling for estimating the position of the work, and upon hearing for judging of the progress of the tool. To enable him to ascertain the depth and general effect of the engraving, he occasionally takes impressions in a black wax, made of bees'-wax and fine charcoal dust, the latter is sifted through muslin and well worked into the wax with the fingers; but the wax is liable to adhere to the fingers, and a more cleanly method is to employ a small piece of blue modelling clay.
For roughing out the work with large tools, as in sinking the body of a large shield, the engine is driven rapidly, and the stone is applied with moderate pressure; in applying the smaller tools the speed employed is slower, and the pressure is less; and for the smallest tools used in cutting the details, the pressure is very slight, and the engine is driven still slower. For greater steadiness in finishing, the seal engraver sometimes puts the foot wheel in rapid revolution, and then, removing his foot from the treadle, stands firmly on both feet while he applies the work, until the tool comes nearly to rest; the foot wheel is then started again, and so on.
From the circular forms of the tools, curved lines and rounded forms, such as are met with in animals, ornaments, and drapery, are more easily executed than designs composed of straight lines, which are cut most readily with tools of as large a diameter as can fairly be applied, but large tools cannot be employed for cutting the corners deeply, and therefore small tools must be used for finishing the corners. To give definition to the engraving, the edges should be left nearly vertical, the amount of bevil required for the relief of the impression, even in deep works, being scarcely perceptible. Fine lines having sharp curves, such as the hair strokes in writing, are very difficult to engrave; they require very small knife-edged tools, and the stone must be applied with great steadiness and delicacy; the bolder lines in German text initials are much more easily managed.
In applying the work to the revolving tool, the stone mounted on the stick is supported and guided in both hands, the stick being held almost vertically below the tool, with the face of the stone upwards, so that both the tool and work are constantly under observation. The stone requires to be held with great firmness, but yet to be applied with exquisite delicacy, especially in cutting the minute details, and considerable practice is required to overcome the difficulties of presenting the stone to the tool with both decision and freedom.
To give steadiness to the arms of the artist, they are supported upon the bench, but the position depends partly upon the form of engine employed, and partly upon the habit of the individual. When the form of engine represented in fig. 1196 is employed, the palm of the left hand is generally rested upon the hemispherical cap of the engine, while the forefinger and thumb embrace the revolving tool, and grasp the upper end of the stick on which the stone is mounted. The thumb and forefinger of the right hand grasp the stick just below those of the left, and the right elbow is supported upon a cushion about 6 inches diameter; this position gives considerable steadiness to the hands, and allows of a free motion in the fingers, between which the stick is, as it were, suspended; it is, however, rather adapted to small than large stones.
When the engine is made more in the form of a lathe head, and overhangs the pillar, a different position of the left hand is generally adopted. In this case the left elbow is supported upon a cushion, in the same manner as the right, the two elbows being widely separated, to lower the hands beneath the tool, and give a wide base to the arms. The left hand is rested against the under side of the overhanging frame, and in some cases the right wrist is supported upon a wooden rest, about 6 inches high and 2 inches diameter, having a hemispherical top to allow of the free motion of the wrist in all directions; and the base of the rest is enlarged to about 4 inches diameter, for greater steadiness. The choice of position is not very material, and depends principally upon habit; but those artists who are accustomed to one position cannot conveniently adopt another. The point of greatest importance is, that both hands should be perfectly steady, and capable of being moved in all directions with great freedom. The wooden rest gives great steadiness to the right wrist, but is liable to interfere with the free motion of the hand, it is, therefore, often dispensed with, except for very delicate works.