LEAD PENCILS. The earliest mention of what • are known to-day as lead pencils ap pears in records dating back to 1565'.—not long after the discovery of the noted graphite mine at Borrowdale. England, in 1554. This mine furnished the material for the first lead pencils. The graphite was sawed into strips and fas tend into wooden casings. In 1795 the Frenchman Conte improved the by grinding the graphite and mixing it with clay, in order to produce grades of hardness and blackness, and this is the method 'of mann facture at the present day. Not all graphite is available 'in making pencils. The variety' known as .'flake graphite) is quite useless, the ' flaky texture allowing the pencil to slip over the paper without leaving a mark. The variety which is used 'is a form in fine scales ap proaching:the amorphous form and is found in localities in Siberia, Bohemia and Bavaria in Europe, and in Mexico. • • The graphite as h comes from the mine is ground in a mill together with a special' kind of clay mined in Germany. This grinding is continued until 'the mass is perfectly homo geneons. The proportion of clay added is deterinitied•hy the degree of hardness. required in the finished 'pencil, the hard (marked • HHHHHH) having the most clay and the very soft (BBBBBB) having hardly any. The soft leads have to be made larger in diameter to stand the strain put upon them when in use. After the grinding, the putty-like mass is put into the cylinder •ef a hydranlic press which has a pierced plate for brittom and a movable plunger•is driven down upon the mass,. forcing it through the perforations in the plate. This operation is repeated as many times as it appears necessary to get the paste into a perfectly smooth condition. It is then, pia into another similar press which has only, one per foration in. the plate. This may he, square, round or oval, depending upon the , shape of . the lead required As the ustnne of lead comes slowly 'through the plate an operator i guides it into a groove cut in a tray and nips it off into lengths of seven inches. When filled, the.trays of leads arecovered with carbon dust and placed in an oven where they are baked at a temperature 'ranging from 2,200° to 2,300° F., to secure just the right degree of hardness. is The wood in which the lead. s encased is red cedar from the • Southern forests—pref erably iii Florida, ,Georgia and Alabama, where the cedar grows with a smooth cheesy texture.
This material is milled until it p.s in seven inches long, twciinches wide and fourth inch thick, sufficient for the lower halves of six pencils. In these slats are cut six grooves: deep enough to hold a string of lead. The slats are given a coat of glue and the leads are put, in place, and, a. cover slat,. slightly thinner, is glued on. The ablocks,) as they are now called, are placed in, damps where,. they remain until thoroughly 'dry and hard. Then 'they into a shaping machine which mills them into six perfectly shaped pencils, round, 'hexagonal, oval or any. other form for which the knives are set' and leaving theni per fectly smooth. Then they are fed into a ma-. chine ,which gives them one or two coats of varnish of Stith a color as desired. The ends are then trimmed a strip of gold leaf laid on one end which receives the 'title from a'notfier Press, the ,tit's bps and robbers ale' put. on:in an automatic machine and the pencils are ready for boxing andlaheling for the market The supply of cedar has been so rapidly. dis appearing that tin attempt. has been made to grow it under cultivation. In 1906 the number of lead pencils made in' theUnited States was about 320,000,000, requiring 110,000 tons of cedar, which was then selling at $20 per ton. Since then cedar, buyers in the South have bought up old cabins .built, of cedar logs, and even replaced old rail• fences with Wire, in order to get the coveted' wood, no 'other sub stance having been proved a satisfactory sub stitute.
The pencils with colored leads go through the same process, except that "China clay" is used as the binder, and colored pigments take the place of the graphite. For these, with their i larger "leads,' it has been found feasible to construct a casing of paper wound spirally around the centre. This is glued at one point on each turn, and the pencils are sharpened by unwinding as many turns as are necessary. The glued spots hold the strip from unrolling all the way down. Copying pencils are made with a coal-tar dye mixed with a gum soluble in water. Carpenters' and markers' pencils have a proportion of wax or tallow incorpo rated with the graphite.