This very useful polishing medium is a natural product, originally obtained from Tripoli, from which it derives its name. It is of a yellowish-grey colour, and its particles are impalpably fine, hence its employment for polishing silver, brass, and other metals. When examined under a powerful microscope, it is found to be composed of the skeletons of animalculae. It is found in Derbyshire, Bohemia, Fiance, Corfu, etc, but that which comes from the latter place is considered by some persons as the best for polishing brass and other metals. It is used either with water or oil, more generally with the latter, and is applied either with a leather or a buff-stick - a flat piece of wood having a strip of soft leather glued to it on one side. In large operations, the polishing is done at a lathe worked by a treadle or steam-power. After using rottenstone and oil in the polishing of articles of jewellery or plate, the article is afterwards "finished" by hand or machine with jewellers' rouge. The rouge is moistened with water, and when this is rubbed on the article previously polished with rottenstone, a brilliant surface is produced with very little labour, and articles of silver, electroplate, gold, and gilt work assume under this treatment the highest degree of brightness which they are capable of receiving. (Watt.)