In making the pots the bottoms are made first. These 
being made to the proper size and thickness, they are turned 
and the knuckle or joint between the side wall and the 
bottom of the pot is formed. The side walls are built by 
“spells,” the potmaker moving from one pot to another in 
his set, and building about six inches to the height of each 
pot every 48 hours. This allows the various spells time 
to stiffen, which prevents the lower spells of the pot from 
sagging. Care also must be taken to see that the upper 
part of each spell is kept moist, in order that the next spell 
succeeding it can be properly kneaded. 
In order to make a seamless wall for the pot, this process 
is continued until the crown is turned in and finished, after 
which the hood is worked on and the pot is thoroughly 
cleaned and smoothed. It usually requires from six to 
twelve months from the time the pot is made before it is 
permissible to be placed in a furnace. 
The manufacture of Tank Blocks is also a long and 
tedious operation. The clay for the various sizes and 
shapes is rammed into moulds by pneumatic clay rammers. 
These blocks are placed in drying rooms, with temperature 
ranging from 90 to 110 degrees, for a period of from one to 
three months, in order to be thoroughly dried before burn- 
ing. They are then placed in large kilns, and burned by 
natural gas, up to a temperature of 2450 degrees Fahren- 
heit. This burning process requires about three weeks time. 
Previous to the organization of the Pittsburgh Clay 
Pot Company, in 1879, there had been but one concern 
in the United States, Thomas Coffin and Company, upon 
which the glass factories had to depend for their supply 
of one of the most important and absolutely necessary 
articles in the manufacturing of glass, namely: glass melting 
pots. 
Recognizing the great growing demand for glass ware, 
and Pittsburgh being the center of this industry, a number 
of prominent glass manufacturers of the Pittsburgh district 
organized the Pittsburgh Clay Pot Company, and pur- 
chased the Hostetter Graphite Factory on South Avenue, 
which consisted of a five-story building 100 x 100 feet. 
In 1883 another five story building 140 x 110 feet and a