PENCILS, BLACK LEAD, MANUFACTURE OF. The best pencils of this kind are made from a natural ore, plumbago, but there are other kinds made of plumbago dust and antimony. The lumps of pure plumbago, when scraped from dirt, are generally of an irregular form, not of a large size. These lumps are cut into thin slices by a circular saw, each slice being sawn by a gauge to its proper thickness. The saw runs vertically and the plum bago is fed below it, the workmen gradu ally raising it, until the slice is cut off, where it falls down slice upon slice of different sizes, upon a table below. One edge is then made straight with a shav ing tool, and it is then fit to be inserted into the wood. The wood is cedar, in half squares cut by a circular saw into the lengths of the pencil. A groove is cut by a proper gauge plane into one side of the wood square, and the workman takes a piece of the cut plumbago, with its edge made straight, and dips it into strong glue and then inserts it into the groove, and then with a very sharp instrument makes a slight cut at each end and gives the plumbago a slight snap, when it breaks off with a clean straight edge. This is again dipped in the glue and ope rated like the other piece, until the whole slice is used up or the pencil groove filled, i when the whole surface is smoothed along and the two pieces are firmly glued toother, forming a rough square pencil. To make it round, it is first forced through a square hole in a steel puppet, by the workman ; and on the other side of this puppet, there is a small planing tool revolving on a centre, with two gauges on it, to turn it round and to the exact size. As soon as the end of the pencil projects from the finishing gauge of the cutters, it is forced into a circular hole in a steel plate, through which it is drawn with a pair of wooden nippers, and it comes out beautifully round pol ished. It is polished by the outer end of
the circular hole being smaller than the the inner, which thus compresses and polishes the wood.
Ever-Pointed Lead. The round pieces of lead for pencil cases are first sawed in to small square pieces, and they are then made round by forcing them lengthways through three circular holes of different sizes cut in pieces of ruby. Inpassing through the first hole, only the four an gles of the prism are cut off, and it is i then octagonal • the next hole is smaller, and it takes oft these eight angles and it then becomes a prism of sixteen sides ; and in the next passage through the small hole, it is made perfectly round. The i plumbago is fed into the ruby by being laid on a groove in a piece of metal, with a steel pin to keep the plumbago from be ing pressed back.
The pure Cumberland black-lead (plum bago) is of too soft and yielding a nature to enable an artist to make a fine clear 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 incorporated, and it has acquired a per fectly uniform consistence. The mass is then sawed 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 hard ness, the materials are differently pro portioned ; the hardest having the most shellac, the softer but very little, and the softest none ; and their blackness is in creased in proportion to their softness.