PENCIL, a name originally applied to a small, fine pointed brush used in painting, and still employed to denote the finer camel's-hair and sable brushes used by artists (Lat. penicillus, brush; literally, little tail), but now commonly signifying a solid rod of marking material used for writing and drawing, either en cased in wood or enclosed in some form of holder.
It has been asserted that a manuscript of Theophilus shows signs of having been ruled with a black-lead pencil; but the first distinct allusion to a pencil occurs in the treatise on fossils by Conrad Gesner of Zurich (1565) who describes an article for writing formed of wood and a piece of lead, or as he believed, an artificial composition called by some stimmi anglicanum (English antimony). The famous Borrowdale mine in Cumberland having been discovered about that time, it is probable that we have here the first allusion to that great find of graphite. While the supply of the Cumberland mine lasted, the material for English pencils consisted simply of the native graphite as taken from the mine. Strenuous efforts were made, however, to render manufacturers independent of the Cumberland mine, whose supplies showed signs of exhaustion. In Nuremberg, where the great business of the family Faber (q.v.) was established in 176o, pencils were made from pulverized graphite cemented into solid blocks by means of gums, resins, glue, sulphur and similar adhesives, but none of these preparations yielded useful pencils. In 1795 N. J. Conte first produced pencils made of graphite which had been ground with certain clays, pressed into sticks and fired in a kiln. This method forms the basis of manufacture of all modern pencils.
Manufacture of Pencils.—Graphite (q.v.) and selected clays are mixed together in proportions determined by experiment and research. The materials are mixed in water and ground in heavy mills. Here is determined quality and degree; the quality by the selection of material and the intensity of grinding; the degree by the proportions of clay and graphite. After grinding, the mass is transferred to a specially prepared filter press and subjected to intense pressure, usually hydraulic, to squeeze out surplus moisture and obtain close texture. The mass so made, of a very firm con
sistency and just plastic, is inserted into heavy power-driven presses to be forced through an aperture of the desired diameter and shape, whence there exudes a thin, still plastic, string-like strip which is laid on boards to dry. After drying, the leads are sealed in crucible boxes and fired in kilns to a suitable heat to vitrify the clay ; the temperature varies from to 1,200° C.
Cedar for Pencils.—Cedar wood is found in many countries, but the fine aromatic, soft, straight-grained wood most suitable for the manufacture of pencils (Juniperus virginiana) comes from the United States. Wood of similar class is grown in large quantities in the parallel belt of Africa, particularly in Kenya, but the Kenya wood is harder, heavier, and inferior to the American variety.
Owing to the steady exhaustion of cedar wood from Virginia, Californian Incense Cedar was introduced to the industry about 1900 and is now largely used for the cheaper grades of pencils. The slats of cedar require careful maturing to prevent warp. They are cut into various widths according to the size and growth of the log, but where possible they are produced wide enough to enable seven pencils to be manufactured simultaneously. The slats are planed and grooved in such a manner that when the two planed surfaces are brought together the grooves form either a round or other aperture which correctly embraces the lead. The surfaces are glued and the boards are clamped in piles, to be subsequently transferred to automatic shaping machines where they are reduced to single pencils, by appropriate machine tools.
The manufacture of "leads" for coloured pencils varies from the method used for the graphite pencils, the basis being kaolin blended with suitable waxes and gums, which are ground together with the necessary colour to obtain the tint required. The firing process is eliminated.
"Copying" pencils used to be constructed on the same lines, with a substitution of aniline dye as the colouring matter. About 1898 improvements were made in copying pencils by blending graphite and aniline dye together. (F. P. Do.)