blower. This blower serves to inject through a tube the carburetted air from a small benzine reservoir attached to it. The incandescence of the point is maintained by this constant injection, and the lines are burnt more or less deeply according to the degree of incandescence, and the pressure applied. The great difficulty is to keep the line of even thickness throughout. The points are to be had of different shapes according to the effect desired. Some are pierced at the end, so that the carburetted air escaping leaves a mark on the leather similar to that which would be produced by a hot iron grazing its surface. In this way a brown tint is obtained varying in darkness in proportion to the proximity of the point to the leather.
6. Blind-stamped Morocco binding with gilt roundels and coloured cameo design. Celsus. De Medicina. Venice, 1477. Italian, 15th Century.
There are also rather large blowers which are worked automatically by compressed air, while others have a pedal action like a sewing machine.
It would be difficult to explain the many ways of handling the point so as to obtain different effects; it should, however, always be held slightly inclined to the right. It is shaped like an eagle’s beak, so that by using the point alone, fine lines of more or less depth are obtained, and by inclining it more to the right the rounded part will burn a larger surface of the leather. Very deep hollows can be made with the point highly heated. Pyrogravure is also an efficient way of depressing the ground work of thick leather when the point is worked with repeated touches over the surface. With a light hand and an accurate knowledge of the degree of heat required to produce fine lines, a skilful artist is able to draw with the point as if it were a pen.
The left hand plays a very important part in the process by controlling the injection of carburetted air through the blower, and thereby regulating the heat of the point. When the incandescence is automatically produced, equal facility in varying the degree of heat according to the requirements of the work is not possible.
POINTOGRAVURE
The following description is borrowed from Mons. E. Aumaître, the inventor of another process for the decoration of leather to which he has given the name of pointogravure.