DISCOVERY OF THE CORNISH STONE. 227 



willing this discovery might be preserved to posterity, if I should 

 not live to carry it into a manufacture ; and with this view, I have 

 thought proper to put in writing, in a summary way, all I have 

 discovered about this matter. 



" The account of the materials used by the Chinese is very justly 

 given by the Jesuit missionaries, as well *as their manner of pre- 

 paring and mixing them into the china-ware paste. They observe, 

 the Chinese have two sorts of bodies for porcelain; one prepared 

 with Petunse and Caulin, the other with Petunse and Wha She or 

 Soapy Eock. The Petunse they describe to be prepared from a 

 quarry stone of a particular kind, by beating it in stamping-mills, 

 and washing off and settling the parts which are beaten fine. This 

 ingredient gives the ware transparency and mellowness, and is used 

 for glazing it. The stone of this Petunse is a species of the granite, 

 or, as we in the west call it, the moor-stone. 



"I first discovered it in the parish of Grermo, in a hill called 

 Tregonnin Hill ; the whole country in depth is of this stone. It 

 reaches, east and west, from Breag to Germo, and, north and south, 

 from Tregonnin Hill to the sea. From the cliffs some of this stone 

 hath been brought to Plymouth, where it was used in the casemates 

 of the garrison ; but I think the best quarries are in Tregonnin 

 Hill. The stone is compounded of small pellucid gravel, and a 

 whitish matter, which, indeed, is Caulin petrified ; and as the Caulin 

 of Tregonnin Hill hath abundance of mica in it, this stone hath 

 them also. If the stone is taken a fathom or two from the sur- 

 face, where the rock is quite solid, it is stained with abundance of 

 greenish spots, which are very apparent when it is wetted. This 

 is a circumstance noted by the Jesuits, who observe that the stones 

 which have the most of this quality are the most proper for the 

 preparation of the glaze ; and I believe this remark is just, as I 

 know that they are the most easily vitrifiable, and that a vein of 

 this kind in Tregonnin Hill is so much so that it makes an excellent 

 glaze without the addition of vitrescent ingredients. If a small 

 crucible is filled up with this stone, or a piece of it put in it, and 

 exposed to the most violent fire of a good wind furnace for an hour, 

 the stone will be melted into a beautiful mass ; all its impurities 

 will be discharged, one part of it will be almost of a limpid trans- 

 parency, and the other appear in spots as white as snow. The 

 former is the gravel, the other the Caulin, reduced by fire to purity. 

 If the fire is not continued long enough to effect this, the upper 

 part and middle of the mass will be of a dirty colour, and the 

 bottom and parts of the sides fine. 



Q2 



