THE PRODUCTS OF CLAY AND FIRE 



methods take much time, and sometimes prove in- 

 accurate from the possibility of mistakes in counting, 

 the potter usually prefers to make his measurements 

 with what he calls a "mixing staff." This is simply 

 a lath with nails driven into it at intervals, each nail 

 representing the height to which each slip of the mixture 

 must reach when the staff is thrust upright into the 

 ark. It makes no difference to the measurer using 

 such a staff, therefore, whether the liquids from 

 the Hungers are pumped, dipped, or run into the 

 ark, as his guide is the rise of the liquid of the mixture 

 along his staff until the indicating nail is reached. 



Of course, since different quantities of each slip 

 are used, the nails in the staff will be placed at unequal 

 intervals, and it is necessary that the slips be run into 

 the ark in a definite order. Usually the lighter ma- 

 terials, blue clay and china clay, are introduced first, 

 to facilitate mixing, followed by flint, stone, and, 

 lastly, the stain. As soon as this last is introduced, the 

 machinery is started and the churning process con- 

 tinued until all the particles of the different substances 

 are held uniformly in suspension throughout the 

 mixture. 



From the mixing ark the slip goes to the "lawns," 

 which, as their name indicates, are sieves made of 

 either silk or wire with fine meshes of a definite size. 

 These are arranged in "lawn boxes " in two or three 

 tiers, one above another, the coarser lawns being at 

 the top where the stream of slip first enters. This 

 straining-out process removes the coarser particles 

 and bits of foreign matter, but there may still remain 



VOL. IX. 1 6 [ 241 ] 



