No. 31,-1885.] 



PLUMBAGO. 



195 



The quality of the Borrowdale ore, dark-coloured, pure and 

 soft, rendered it eminently suitable for pencils of the finest 

 descriptions, and for about two and a-half centuries the world 

 was practically supplied with pencils from this one source. 

 From one pound of the ore, worth 305., or at the rate of 

 £168 per cwt., the number of pencils cut averaged from 18 

 to 20 dozens. The mineral was stated to be found in pipes, 

 strings, and irregular masses called " sops," a description 

 which, substituting modern terms for olden, applies equally 

 to the Ceylon graphite formations. Since the exhaustion 

 of the Cumberland mines, the best ore for pencils is said in 

 some books to be obtained from Siberia, while no doubt the 

 m'assive and soft stove polish black lead, occurring in various 

 parts of Germany — Bavaria, Bohemia, &c— is applied 

 to the manufacture of pencils. It cannot be questioned 

 also that some of the finest quality Ceylon plumbago is 

 thus used in Britain, and also in the United States, 

 notwithstanding directly contradictory statements on the 

 subject, one writer declaring that the presence of grit or 

 iron rendered the much-lauded Siberian mineral unsuitable 

 for pencil manufacture ; while another, with equal posi- 

 tiveness, writes that, notwithstanding the acknowledged 

 purity of Ceylon plumbago, it is not applicable to pencil- 

 making. 



The old method of making pencils was to saw blocks of 

 so-called black lead into strips to be inserted in cedar wood 

 cases, but now the general mode of manufacture— and this 

 applies to crucibles as well as pencils-— is to grind and 

 comminute the ore as finely as possible, and then after 

 washing and intermixing with definite proportions of certain 

 qualities of clay, also ground fine, to subject the mixture 

 to tremendous pressure and to a baking process. For 

 blocks composed solely of black lead dust, prepared for 

 pencil-making, the air-pump has also been utilized to 

 render the blocks perfectly solid. Germany, besides 

 supplying the form of so-called " black lead" suitable 

 for stove polish and pencils, yields also a peculiar kind 

 of clay, which in the United States at any rate is used to 

 give adhesiveness to the ground particles of plumbago when 

 subjected to the extreme pressure which has been mentioned. 

 Secrecy is, I believe, observed at the Battersea Crucible 



