1900.] on Pottery and Plumbism. 401 



The capillarity of the porous biscuit draws iu a certain amount 

 of the cream-like liquid, causing the deposition upon its surface of 

 a thin film of the glazing material. The article is then allowed to 

 dry, is trimmed or cleaned, if necessary, to remove any aggregation 

 or superfluity of the glazing material from its edges, or other pro- 

 jecting parts, and again placed in the " saggers," and re-heated in 

 another oven, technically known as a " glost oven," so as to cause 

 the glazing material to fuse, and spread evenly over the body of 

 the ware as a transparent vitreous covering. If the article is 

 decorated by a coloured design, this is usually done before dipping, 

 the iw biscuit " being either painted in so-called underglaze colours, 

 or the design transferred to it from a lithographic print, or other- 

 wise manipulated, depending on the character of the decoration. 



(The lecturer here exhibited several slides upon the screen of 

 photographs lent by the Eev. Malcolm Graham, vicar of St. Paul's, 

 Burslem, and Mr. J. H. Walmslcy, H.M. Inspector of factories, Stoke. 

 These showed groups of workpeople engaged in the various processes 

 of the manufacture of pottery in which lead is used.) 



Proceeding, he said : — Some judgment is required in the selec- 

 tion of the materials needed to form an aj^propriate glaze. The 

 glaze to be efficient should be clear, transparent and lustrous. 

 It should not only be without injurious action on any colours it 

 may have to cover, but ought, if possible, to enhance their brilliancy. 

 It must be sufficiently thin, and of a proper degree of fusibility, so 

 as not to interfere with or impair any modelling on the ware. It 

 must be sufficiently hard and insoluble to resist a fair amount of 

 wear, especially in culinary articles, or those intended for general 

 domestic use ; and it must not be attacked by such acids as may be 

 found in food. Lastly, it must not " craze " : that is, it must have 

 substantially the same thermal expansibility as the body of the 

 article to which it adheres, otherwise it will chip off, or break up 

 into cracks. Crazing not only renders the ware unsightly, but causes 

 it, in the course of time, especially in the case of culinary and table 

 ware, to absorb oils and fats, &c, and thus to become unclean, and, 

 it is said, to harbour even the ubiquitous microbe. 



These conditions are, on the whole, fairly well realised in 

 ordinary earthenware. It is, however, in hard porcelain, and more 

 especially in the masterpieces of Oriental manufacture, and in the 

 produce of the leading Continental factories, and, to a large extent 

 in the soft porcelain made in this country by the best makers, that 

 the finest results are obtained. This, in the case of hard porcelain, 

 is due mainly to the circumstance that the chemical nature of the 

 glaze more nearly approaches that of the body of the ware than is 

 the case with earthenware, and that at the high temperature at whicli 

 the porcelain is fired, there is a more complete interfusion of the 

 glaze and the biscuit. 



Moreover, the glaze of hard porcelain, being practically fused 

 felspar, is harder even than glass, and much more resistant to the 



