INGENUITY AND LUXURY 



the number of small objects fired without extra cost 

 may amount to several thousand at each firing. 



In this way the pottery manufacturer effects a very 

 great saving, since firing is about the most expensive 

 single item in the process of pottery-making. 



Firing consists in raising the temperature of the oven 

 gradually and uniformly to a certain point, usually 

 about 2,500 F. The degree of heat varies for different 

 purposes, but even the very lowest is so high that it 

 takes many hours of firing, and many tons of coal, 

 to reach it in the great sixteen- or twenty-foot ovens. 

 Furthermore, in ovens of that size the variation in 

 temperature in different parts might be enough to " over- 

 fire" and spoil ware in one part of the oven, while in 

 another part the ware would be "under-fired," if the 

 fireman were careless or ignorant, or if he had no way 

 of ascertaining approximately the temperature in every 

 part of his oven at all times. 



Of course where such high temperatures are at- 

 tained the use of ordinary thermometers is out of the 

 question, but the potters have discovered other means 

 of determining the heat of the ovens which are exact 

 enough for practical purposes. An experienced fire- 

 man can tell a great deal about the oven temperature 

 by the appearance of the heated interior; but even the 

 most skilful workman does not trust to this test alone 

 unless forced to do so by some accident. Most firemen 

 make use of little rings of clay called "trials" for 

 determining the temperature. These are placed in 

 various parts of the oven, the usual method being to 

 put them into saggers which have holes cut in one 



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