THE POTTER'S ART. 



Fig. 40. 



drawing the flames to this point, where they enter the oven : other 



flues, termed "bags," pass up 

 the internal sides to the height 

 of about four feet, thus conveying 

 the flames to the upper part. 



When " setting in " the oven, 

 the firemen enter by an opening 

 in the side, carrying the saggers 

 with the ware placed as described : 

 these are piled one upon another 

 from bottom to top of the oven, 

 care being taken to arrange them 

 so that they may receive the 

 heat (which varies in different 

 parts) most suited to the articles 

 they contain. This being con- 

 tinued till the oven is filled, the 

 aperture is then bricked up : 

 the firing of earthenware bisque 

 continues sixty hours, and of 

 china forty-eight. 



The quantity of coals necessary 

 for a "bisque" oven is from 16 

 to 20 tons ; for a " glost " oven from 4| to 6 tons. 



The ware is allowed to cool for two days, when it is drawn in 

 the state technically termed "biscuit," or bisque, and is then 

 ready for "glazing," except when required for printing, or a 

 common style of painting, both of which processes are done on 

 the "bisque" prior to being " glazed." 



8. A porcelain oven of three stages, used in the Sdvres manu- 

 factory, is represented in fig. 41 and fig. 42, the former being the 

 exterior view, and the latter a vertical section by a plane through 

 its centre. Each of the lower stages, L and L', is heated by four 

 furnaces, from which the flame and heated air is drawn into the 

 oven through the flues g. Fire-doors of plate-iron are provided, 

 by which the mouths of the furnaces and ashpits can be closed 

 or opened at pleasure. 



When the several stages of the ovens are charged with the 

 wares to be baked, the firing is conducted so as to raise the 

 temperature by slow and regulated gradation. The fires, at first 

 moderate in their force, are constantly augmented for from 

 sixteen to twenty hours. "When the oven is thus well heated, the 

 great firing is commenced by giving full charges of fuel to all the 

 furnaces. The oven itself, which is cylindrical below, terminating 

 in a conical roof with an opening at top, governed by a regulating 

 188 



