No. 31.— 1885.] 



PLUMBAGO. 



is for making pencils. Originally, lumps of the mineral 

 were cut into the required shape. Then, un til the Borrowdale 

 mines gave out, the masses were sawn into thin pieces to 

 be enclosed in wood. And now Mr. Cleveland proceeds to 

 describe, in detail, the process of which, according to the 

 latest edition of the Encyclopaedia Britannica, M. Conte, of 

 Paris, was the discoverer : — 



" The present method consists in selecting the best granulated 

 plumbago (found till recently only in Germany), pulverizing it 

 very finely, and floating it in water through a series of vats ; the 

 coarser particles settle to the bottom of the first vat, the finer in 

 the next, and so on, till, after passing through several, that which 

 settles in the last vat is considered fine enough for the purpose. 

 A suitable clay is found as yet only in Germany, and this is 

 treated by the floating process, the finest only being fit for use. 

 The plumbago and clay are then mixed together with water to 

 the consistency of cream, ground together like grinding paint. 

 When the operation is completed, the mass is plastic, water 

 enough having evaporated to leave it in that state. It is then 

 placed in a press and forced through an opening of the size 

 desired for the pencil leads, and the leads are cut to a suitable 

 length, straightened, and dried. When dry enough to handle, 

 they are placed in a crucible, the air excluded, and subjected to 

 a high heat, which bakes them and brings them out ready to be 

 placed in the cedar for pencils. The different grades are produced 

 by the different mixtures of clay and plumbago ; the more clay, 

 the harder the grade produced. Skill in the manipulation, the 

 exercise of great care as it progresses., and an expert to select the 

 materials, are absolute prerequisites for a perfect product." 



It will thus be seen that the finishing process in the 

 manufacture of black lead pencils is baking in a crucible 

 composed, probably, of the same mineral. 



In most of the works consulted in the preparation of this 

 paper— and they have been many and various — the credit of 

 having first made and used plumbago crucibles has been 

 given to the Germans. Mr. Cleveland awards the credit to 

 '* the Dutch, and it is certainly significant that the Dutch 

 name for the mineral should be potloot, or pot lead, the 

 lead of which crucibles are made (?) — Mr. Cleveland states 

 (writing some six years ago) : — 



4t Crucibles or Melting Pots, Retorts, fyc. — Forty years ago 

 the only plumbago crucible was made by the Dutch, the melting 



f2 



