(6) The mathematical, instrument makers treat it as brass - that is, for flat work they first use water of Ayr stone, and then rotten-stone and oil. Turned work is polished in the lathe with rotten-stone and oil, taking care not to use too high a speed, which would heat the work. Some use lampblack and oil to finish with where a very high polish is wanted, or the bare palm of the hand, as in getting up silver plate. Chain and ornament makers use circular buffs for their flat work, made of seahorse-leather, and for work of irregular forms, buffs of calico. A number of pieces, 12 in. in diameter, are screwed together between flanges, like a circular-saw spindle, and used with rotten stone, always taking care not to heat the work; brushes are not at all suitable for it.