A stone and muller is a hand-operated tool used for mixing and grinding paint

Paint

Paint is any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. One may also consider the digital mimicry thereof...

. The stone and muller was popular with artist

Artist

An artist is a person engaged in one or more of any of a broad spectrum of activities related to creating art, practicing the arts and/or demonstrating an art. The common usage in both everyday speech and academic discourse is a practitioner in the visual arts only...

s and tradesmen

Tradesman

This article is about the skilled manual worker meaning of the term; for other uses see Tradesperson .A tradesman is a skilled manual worker in a particular trade or craft. Economically and socially, a tradesman's status is considered between a laborer and a professional, with a high degree of both...

 from the late 18th through the 19th century. A stone and muller differs from a mortar and pestle

Mortar and pestle

A mortar and pestle is a tool used to crush, grind, and mix solid substances . The pestle is a heavy bat-shaped object, the end of which is used for crushing and grinding. The mortar is a bowl, typically made of hard wood, ceramic or stone...

in that the former consists of two flat stone surfaces which are rubbed together to create a paste, whereas the latter consists of a bowl and stick.