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Plumbago Or Graphite Contains In Spite Of Its Name No Lead Being

simply a species of carbon or charcoal. In most specimens iron is
present, varying in quantity from a mere trace up to five per cent,
together with silica and alumina. Sometimes manganese and titanic acid
are likewise found. It is curious that carbon should occur in two
distinct and very dissimilar forms--as diamond, and as graphite; one,
white, hard, and transparent; the other, black, soft, and opaque: the
artist, therefore, who uses a pigment of plumbago, paints with nothing
more or less than a black diamond. The best graphite, the finest and
most valuable for pencils, is yielded by the mine of Borrowdale, at the
west end of Derwent Lake, in Cumberland, where it was first wrought
during the reign of Elizabeth. A kind of irregular vein traverses the
ancient slate-beds of that district, furnishing the carbon of an
iron-grey colour, metallic lustre, and soft and greasy to the touch.
Universally employed in the form of crayons, &c. in sketching,
designing, and drawing, until of late years it was not acknowledged as a
pigment: yet its powers in this respect claim a place for it. As a
water-colour, levigated in gum in the usual manner, it may be
effectively used with rapidity and freedom in the shading and finishing
of pencil drawings, or as a substitute therein for Indian ink. Even in
oil it may be employed occasionally, as it possesses remarkably the
property of covering, forms very pure grey, dries quickly, injures no
colour chemically, and endures for ever. These qualities render it the
most eligible black for adding to white in minute quantity to preserve
the neutrality of its tint.

Although plumbago has usurped the name of Black Lead, there is another
substance more properly entitled to this appellation, and which may be
used in the same way, and with like effects as a pigment. This substance
is the sulphide of lead, found native in the beautiful lead ore, or
Galena, of Derbyshire. An artificial sulphide can be prepared by dry and
wet processes, which is subject to gradual oxidation on exposure to the
air, and consequent conversion into grey or white. Neither variety can
be compared to graphite for permanence, although the native is
preferable to the artificial.

Plumbago, or the so-called Black Lead, is often adulterated to an
enormous extent with lamp black.


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