INCISING THE LEATHER
This being the first operation in working thick leather by carving, engraving and modelling, it will be dealt with before passing to the different processes peculiar to these methods of decoration. The incising is done after the design has been traced. There are numerous incising knives for the purpose which vary in shape and are manipulated in different ways; no one of them can be specially recommended as notably superior to the rest, and the artist should choose the one with which he feels most likely to succeed. The knife illustrated in Fig. 2 is used with a downward movement and is held—as shown in Fig. 3—very short, so as to obtain a sufficient purchase over the blade which is guided by the middle finger. The knife illustrated in Fig. 4 is used upwards. Fig. 5 shows the manner in which it should be held to produce a vertical cut. It will be found of great assistance in making a good firm cut to guide the right hand
with the left hand as in Fig. 5. When curved lines are to be cut, the left hand must be used to turn the leather so as to present it in the most favourable position for the operation of the blade. The third knife (Fig. 6) is held like a graver with the handle supported against the palm of the hand and is pushed forward (Fig. 7). It is useful in cutting curved lines over a large surface. The depth of the incision should vary according to the effect
to be produced by the subsequent operation, but it should never exceed a third of the thickness of the skin.
2. Casket covered with stamped leather, cuir bouilli. German, 14th Century.
FIG. 2, FIG. 3.—INCISING KNIFE USED DOWNWARDS LIKE A PENCIL
Thin skins should rarely be cut, and, if they are cut, the incision should barely penetrate the surface. On ox-hide the depth of the cut may be considerable without danger of impairing the strength of the leather.
FIG. 4, FIG. 5.—INCISING KNIFE USED UPWARDS
When the leather is to be modelled in high relief, the design should be well separated from the background in the cutting process. The incision should also be deep when the outline is to be accentuated afterwards with a
tool called an “opener” (Fig. 9) to produce an effect like the leading in stained glass.
Should it be desired to raise and turn up the edge of the leather to simulate a leaf, petal, or piece of ribbon detached from the background, the knife must be held slanting, as in Fig. 8, so as to make an almost horizontal cut.
FIG. 6, FIG. 7.—INCISING KNIFE HELD LIKE A GRAVER AND PUSHED FORWARD
However thick the leather may be, it is important that two lines should never be cut quite up to the point of intersection. For example, in cutting the outline of a leaf, the points of the indentations should be left uncut to avoid the tendency of the part within the angle to project and turn back. Sufficient impression can be
obtained with the modelling tool to give a finished effect to these points.
FIG. 8.—EXECUTING A SLANTING CUT WHEN THE EDGE OF THE LEATHER IS TO BE SUBSEQUENTLY TURNED UP
The incision must be clean and sharp, and absolutely vertical, except where it is made slanting for the purpose described above.
3. Coffret covered with leather, incised, coloured and gilt. French, 14th Century.