Black Lead
2 of the 7 encyclopedias on this shelf carry an entry for Black Lead. Both are reproduced below, so you can see where they agree and where they differ.
The Encyclopedia of Founding (1892)
The name commonly given to plumbago, or India-silver lead-facings. It is called "India silver" because it is mined in India, on the island of Ceylon, and because it yields a polish of a silvery tone. The Jos. Dixon Crucible Company classify the several kinds as: Plumbago-facing for common work; German or Bohemian lead for flat moulding; Ex, Ex, plumbago-facing for stove-plate, printing and copying presses; India-silver lead for light and ordinary job-moulding; "XX," plumbago for heavy cast-iron and steel castings; and Founders' core-wash for cores, loam, and dry-sand work--at prices from 10c. to 3 1/2c. per pound, in the order given. One kind works with dry sand, and is used as a wash; another works with green sand, and through a shake or blacking-bag; still another, with green sand, to be laid on the surface with a brush. Some facings require, for perfect lines, a little dusting of powdered charcoal. Some brands will slick with the tools; others not--making it necessary for the parties ordering these facings to specify what use they intend to put them to. Such kinds as admit of easy slicking on green-sand moulds are the most useful; as when this operation is properly done with good material, it will neither burn nor run before the molten metal, but adhere firmly to the sand surface, causing it to part clean from the casting, giving it a uniform bright color. See FACING; GRAPHITE. Black Sand is sometimes termed "old sand," and is the sand which constitutes what is called the foundry floor. When first introduced into the foundry the new sand is usually of a yellow or brownish color, sometimes red; but by subsequent use for casting purposes, it becomes burnt, or "old." The facing mixtures, containing sea-coal dust, is gradually insinuated among the floor-also; these, along with the constant use of charcoal and lead-facings, cause the change in color of the original sand. For all parts of thin castings, which are far removed from the gates, this old sand, if fine originally, is to be preferred as a facing, because the constant burning to which it has been subjected has eliminated all clayey and other deleterious ingredients; thus forming a surface upon which the molten iron will placidly rest free from the disturbing influences of the gas-producing substances ordinarily found in new-sand. See NEW-SAND; FACING-SAND; FACING.
Collier's New Encyclopedia (1921)
GRAPHITE, or for it seemed probable that the business PLUMBAGO, a mineral consisting chiefly of carbon, but containing also more or less of alumina, silica, lime, iron, etc., to the extent of 1 to 47 per cent., apparently mixed rather than chemically combined. Black lead is the popular name, and that by which it is generally known in the arts, though no lead enters into the composition of the mineral; graphite is that generally preferred by mineralogists. It sometimes occurs crystallized in flat hexagonal tables; but generally massive, and more or less radiated, foliated, scaly, or compact. It is of a grayish black color, with a somewhat metallic luster, and a black and shining streak, and is perfectly opaque. It is greasy to the touch, and is a perfect conductor of electricity. It occurs in beds and masses, laminæ or scales in the (gneiss, mica schist, clay schistose rocks slate, etc.), and is sometimes in such abundance as to give its name to the schist (graphite schist) in which it appears. Thick, vein-like masses of black lead are met with in Siberia, Spain, Canada, New Brunswick, United States, Ceylon, and elsewhere. It is far more incombustible than even anthracite (or blind coal), on which account it is much used for the manufacture of crucibles or melting-pots. These are half clay and black lead. Black lead is employed for making pencils. It is also extensively employed to give a black gloss to iron grates, railings, etc., and to diminish the friction of belts, machinery, and rifle cartridges.