40 Transaciions of the 



the health of the workmen employed, who are frequently seized 

 with paralysis, and because the lead, which is soluble by means of 

 acid, and deadly poisonous, renders vessels thus glazed improper 

 for preparing or containing many articles of human food. The 

 bad effect of raw glazes upon their health is greatly lessened to 

 the workmen when they can be brought to the frequent use of 

 ablutions. In every pottery the men employed in glazing are 

 plentifully supplied with soap, which they are enjoined to use 

 before quitting their work. Glazes for porcelain and the finer 

 kinds of earthenware are generally made with white-lead, ground 

 flints, glass, and common salt, Lyme sand, combined with soda as 

 a flux, being frequently added to the ingredients just mentioned ; 

 but as almost every manufacturer uses a different glaze, and the 

 recipe is kept secret to himself, under the impression of its 

 superiority compared with that used by his competitors, it is not 

 possible to state proportions with accuracy. 



The French porcelain makers have given the composition of 

 hard glazes made by them, which are all said to be formed of 

 flint, ground porcelain, and crystals of calcined gypsum in the 

 following different proportions : — 



No. 1. No. 2. No. 3. 



Calcined flint, . . 8 parts. 17 parts. 11 parts. 



Ground porcelain, . 15 „ 16 „ 18 „ 



Crystals of calcined gypsum, 9 I„ 7 „ 12 „ 



It is necessary to vary the composition of the glazes in order 

 to suit the different materials that form the body of the ware. 

 The quantity of lead which enters into the composition of the 

 better kinds of glazes is so small, that the deteriorating and per- 

 nicious effects which attend the use of raw glaze need not be 

 apprehended from their application. The saggars used to enclose 

 the wares, when baked in the gloss-oven, are similar to those 

 employed in the first firing. Previous to their insertion the 

 pieces must have the glaze wiped from the parts which imme- 

 diately rest upon the bottoms of the saggars, otherwise they would 

 adhere, and might be broken on their removal. The cases are 

 piled up in the manner already described, and just that degree 

 of heat is employed which will give perfect fusion to the glaze, 

 and cause it to spread regularly over the surface, the temperature, 

 of course, varying according to the quality of the articles and the 

 composition of the glaze. The temperature of the gloss-oven is 

 generally about 1300 degrees less of Fahrenheit than the heat of 

 the biscuit-oven. The glaze, as seen in the finished porcelain, 

 should not impart a lustrous appearance, but, while beautifully 

 smooth to the touch, should present to the eye rather the soft- 

 ness of velvet than the gloss of satin. This peculiar semblance 



