These bisque moulds have been handmade by Clae. 
Slump moulds are a good way to reproduce a specific size or shape when you are hand-building bowls or cups. 
Bisque moulds are lighter and sturdier than plaster moulds, and are much easier to clean.
 
Clae Bisque moulds come in 2 sizes:
 
04  17cm in diameter and 9cm tall
05  23cm in diameter and 12cm tall
 
Note that because these moulds are made by hand there is some variation in measurements between each mould.