There is no necessity for keeping all the lines of even thickness. For instance, provided the character of the form is not altered, the outline on the shaded side may be made thicker than on the illuminated side; also distance can be indicated by the use of thinner lines, for these, although really black, will give the impression of greyness. Then again, a line may be drawn with local increases and decreases in thickness, as in ordinary writing, and such lines drawn by a skilled hand can be made to express a marvellous amount of modelling.
Fig. 13. Sea Lavender (Statice Limonium). After Matthiolus.
(From Hatton's Craftsman's Handbook.)
The draughtsman, however, is not restricted to lines; any marks which can be made with a pen and black ink may be employed, provided they be sufficiently firm and large.
The accompanying figure (14) which is a reduction of an illustration in Church's Floral Mechanisms, illustrates the use of lines of varying lengths for shading.
