|
|
Page 180:-
become an ingredient in several anti-attrition compositions; but
effects have been formerly attributed to it in dying, and
medicine, which were perhaps only imaginary. Yet its principal
use is in pencils, for which Keswick has long been famed; and in
their manufactory great improvements have lately been made; but
though in the vicinity of the mine, the pencil-makers are obliged
to purchase all their black-lead in London, as the proprietors
will not permit any to be sold until it has first been lodged in
their own warehouse. It was formerly used without any previous
preparation; being only cut with a saw to the scantlings
required, and thus enclosed in a suitable casing of cedar wood:
but generally being too soft for some purposes, a method of
hardening it had long been a desideratum; and a process has at
length been discovered, by which it may be rendered capable of
bearing a finer and more durable point; but its colour will be
somewhat deteriorated.
Great quantities of pencils are now made of a composition, formed
of the saw-dust and small pieces of black-lead, which being
ground to an impalpable powder, is mixed with some cohesive
medium: for this purpose different substances are employed, some
of which make a very inferior pencil; but others, being united at
a proper degree of heat, and consolidated by a strong pressure,
make a pencil to answer for many purposes, (especially where the
writing is intended to be permanent,) full as well as the genuine
black-lead.
|
