Stage 4 - Making the Slip
Slip is a suspension of clay and other materials in water. For vitreous china slip, the materials included china clay from Cornwall, Ball Clay from Devon, North Cape Nepheline Syenite (NCNS) from Norway, Silica Sand from Chelford and ground pitchers which could be made from fired pieces scrapped later in the process. All raw materials were tested by the Lab as they were received to ensure they conformed to the specifications.
Smaller amounts of fine fireclay slip were used in production in later years but this was normally purchased rather than made on site.
Using a monorail system a weighed amount of each material was transferred into a large mixer called a blunger which contained water. After mixing the virgin slip would be transferred into further tanks (arks) to age before being blended into the casting slip system.
Scrap clay pieces were also separately returned to the sliphouse and mixed with water to remake slip (known as scrap slip) which would also be blended back into the casting slip.
Each batch of slip was tested by the Lab to ensure it was to the correct specification before being released into the production system.