Rottenstone, also spelled rotten stone and known as tripoli, is finely powdered rock and is used as an ultra-fine polishing abrasive in French polishing.
The rottenstone is applied with a light oil such as linseed oil and a cotton or felt pad. First dip the pad into the oil first and then into the rottenstone, using moderate pressure rub along the grain until the desired amount of sheen is achieved. Wipe off the excess with a clean cotton cloth and then wipe over with a cloth dampened in white spirits to remove the oil film.
For an aged effect on gilded surfaces lightly dust the surface with a soft brush, then blow off or lightly brush away the excess rottenstone, leaving the dust in the recesses.