A tool employed for holding or grinding substances upon a stone. The glass-grinders thus call the instrument used for grinding their glasses, which consists of a round piece of wood, about six inches long, to one end of which is cemented the glass to be ground, whether convex in a basin, or concave in a sphere. For grinding colours, the muller is of stone, and is usually employed upon a flat slab of stone; as may be seen in most painters' and colourmen's shops. An improvement upon this plan was, however, introduced by Mr. Rawlinson, for which the Society of Arts awarded him their silver medal. As this machine is said to have been proved, by many years' experience, to be more effectual and expeditious in grinding colour to that extreme fineness required by artists, and to be less prejudicial to the health of the workman, we shall here add a description of it.

The machine consists of a short cylinder of black marble, 16 1/2 inches in diameter, and 4 1/2 in thickness, turned vertically on its axis by means of a winch. A concave piece of marble is provided, of the same breadth as the circular stone, and forming a segment of the same circle, one-third of the circumference in extent; this segment, which may be considered as the muller, is fitted into a solid piece of wood of a similar shape, one end of which is secured by a hinge, or otherwise, to the frame; the other end rising over the circular stone, and supported by it, is further pressed down on it by a long spring bent over from the opposite extremity of the stand, and regulated as to its pressure by a screw, whose end turns against the concave muller. A slight frame of iron in front, moveable on a hinge, supports a scraper, formed out of a piece of watch-spring, which takes off the colour, and is turned back out of the way when not in use.