Glass Muller and Slab for Grinding Pigments

Painters and colourmen grind pigment into oil or gum with a muller, a heavy bell of glass or stone with a flat face, rubbed over a slab; Andrew Ure (1839) describes indigo and gold leaf ground this way. Gather glass rod into a solid bell in the flame, anneal it, then grind its face and a glass slab against each other with grit so they bite. The picture: grinding a red pigment with a glass muller.