These are instruments for marking, drawing or writing, formed of
graphite, colored chalk or materials of similar properties, and having a
tapering end, inclosed, generally, in a cylinder of softwood. Fig. 167
represents a ruling pencil; its point is a parallelogram or of a wedge
shape. In ruling, the length view rests against the square; its shape
gives considerable strength to the lead and allows the making of a very
fine line. Fig. 168 differs in the point of the pencil shown, as may be
observed in the illustration.
A pencil that is hard is best for mechanical drawing; one that will
retain a good point for some considerable time. Pencil lines should be
made as light as possible; the presence of lead on the surface of the
paper tends to prevent the ink passing to the paper, and in rubbing out
pencil lines the ink is reduced in blackness, and the surface of paper
is roughened, which is a disadvantage. As little erasing or rubbing out
as possible should be done.