Without a complete sentence it's very difficult to know how to translate "Mitarbeiter der ..." One possibility would be employees involved in ceramic body preparation.

body preparation
http://books.google.com/books?id=8V4VHrOGSSUC&pg=PA422&lpg=P...

Star Porcelain Co., a contract manufacturer of technical ceramic parts, has discontinued all manufacturing operations at its Trenton, N.J., facility. Star has contracted exclusively with Mohr Corp. for the liquidation of all machinery, equipment, furniture and fixtures. Available for sale by private negotiation are automatic mechanical Stokes 20-, 12- and 4-ton presses; a complete ceramic body preparation system using the muller mixing and rotary dryer processing methods; a water reclaim and filtration system; and more.

http://www.ceramicindustry.com/Articles/Industry_News/e0076d...

Body (G&W)
The term used to describe clay and any inclusions present in it, particularly prior firing, though it may also be used to describe the finished product. Synonymous with fabric and sometimes, but not always, paste.
Body (Stoltman 1991)
The bulk composition of a ceramic vessel, including clays, larger natural mineral inclusions in the silt, sand, and gravel size ranges, and temper. Synonymous with fabric
http://www.tulane.edu/~kidder/Anth 461/ceramic terms.html