Scientific American 45, 27.7.1850
The pure Cumberland black-lead (plumbago) is of too soft and yielding a nature to enable an artist to make a fine clear line; to produce, therefore, a pencil that will effect this, a hard resinous matter is intimately combined with the lead in the following way: - Fine Cumberland lead (in powder) and shellac are first melted together by a gentle heat; this compound is then reduced to powder again, then re-melted, then powdered again, and re-melted until both substances are perfectly uniform consistence. Tha mass is then saved into slips, and glued into the cedar mountings, in the usual manner of making other black-lead pencils. To render them of various degrees of hardness, the materials are differently proportioned; the hardest having the most shellac, the softer but very little, and the softest none; and their blackness is increased in proportion to their softness.
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