From twenty to forty cubic yards of the material
can be thus washed by one wash mill in a day.
Care leaded with Shale Going up Incline to Dry Shed
Sometimes the clay is obtained in the form
of shale or is hard and lumpy so that it has to
be dried and crushed before it is mixed with water.
Crushing is accomplished in a drypan or pan mill
equipped with edge rollers. The pan mill consists of
a circular iron pan, six to eight feet in diameter
and perhaps one foot deep, in which a pair of
heavy wide wheels are caused to roll. These
wheels or rollers move in a circle just inside the



92 ELEMENTARY INDUSTRIAL ARTS

edge of the circular pan. The wheels are called
edge rollers because they have a narrow tread
which provides a cutting action in crushing
shale which is ground while dry. Much grinding
and crushing is often avoided by exposing the clay
to the action of the weather for a considerable



Feeding a Drypan

length of time before any attempt is made to
work it.
After the clay has been washed it is tempered.
Tempering consists in mixing water with the
clay and working the two together until a paste
of fairly uniform consistency is formed. The
best results are obtained when the clay is tem-
pered for two days before it is pugged.
