600 Manufacture of 



of Chinese workmen, it may hereafter become an article of manufac- 

 ture in India. I also found it in considerable abundance, and nearly of 

 equal purity on the Neilgherries. 



Report upon the manufacture of Pottery and Porcelain in South India, 

 by Captain J. Campbell, Assistant Surveyor General, dated Rya- 

 cotta, 22d September, 1841. 



1 . All the varieties of Pottery and Porcelain are composed of silica 

 and alumina in varying proportions, but as these earths are perfectly 

 infusible in the strongest heat, the mixture could not therefore be 

 aggregated together into a compact mass, without the aid of some 

 substance which would partially fuse it. 



2. Lime has the property of rendering a mixture of silica and 

 alumina very fusible, and it is therefore used in the proportion of 

 about one per cent, in the finest kinds of Porcelain, to which with the 

 aid of a little potass, and a very high heat, it imparts that degree 

 of semi-transparency, by which they are distinguished from what is 

 generally called Earthenware. 



3. Earthenware differs from Porcelain principally in containing 

 more alumina, by which it is easier hardened in baking, but is always 

 more or less porous, in consequence of which, it requires to be cover- 

 ed with a fusible varnish or glaze. 



4. As the pure earths are seldom found in nature in a finely com- 

 minuted state, the materials for Porcelain and Pottery are derived 

 from various earths and clays, by the admixture of which the proper 

 proportions of the ingredients are insured. By the scientific opera- 

 tor, the knowledge of the component parts of the materials is deriv- 

 ed from chemical investigation and analysis ; by the merely practical 

 man, from repeated trials of the properties of various mixtures when 

 subjected to a strong heat. 



5. In Porcelain, the principal material used is kaolin earth, found 

 in Cornwall and in various parts of the continent, and which is 

 generally considered by Geologists as decomposed or decayed granite, 

 decomposed felspar, decomposed mica, and several other rocks ; but 

 which probably owes its origin to none of these, being particularized 



