THE POTTER'S ART. 



consistency that it could not be worked on the potter's wheel, and 

 was even moulded not without much difficulty. 



To give it sufficient tenacity and consistency to prevent it from 

 cracking or crumbling to pieces in the process of moulding, it was 

 mixed with about twelve per cent, of its own weight of a mixture 

 of black soap and parchment size, the soap at a later period being 

 replaced by a solution of tragacanth gum, to which are attributed 

 the saline efflorescences which were occasionally manifested on the 

 articles fabricated. In the process of turning the moulded pieces 

 a saline and silicious dust was produced, which was extremely 

 injurious to the potters, and caused asthmatic and pulmonary 

 complaints. This was one of the reasons why the fabrication of 

 tender porcelain was the more readily discontinued after the 

 discovery of kaolin. 



Owing to the want of plasticity and coherence in this artificial 

 paste, great difficulties were encountered in the several stages of 

 its manufacture. The want of tenacity rendered it necessary, 

 when the articles were placed in the oven, to support all the pro- 

 jecting parts during the process of baking ; and, in order that the 

 forms of these parts might not be distorted, it was necessary that 

 their supports should be formed of the same paste as the articles 

 themselves, so that the whole mass, including the supports, might 

 contract together. The linear dimensions contracted in the baking 

 by one-seventh, and, consequently, the bulk or volume of the 

 article was diminished in the proportion of three to two. 



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