The first step in the polishing of metals consists in rubbing down the surface by some hard material that will produce a series of scratches in all directions, the level of which is practically identical, and which obliterate file-marks. For this purpose pumice and water or sand and water applied upon a piece of soft wood is used. After the removal of the first coarse marks the next step is the removal of the marks left by the first polishing material by means of finely-powdered pumice-stone ground up with olive oil. To proceed with the polishing even finer powders are next used, such as tripoli and rotten stone. For the higher degree of polish putty of tin and crocus martis are also used. The entire process consists simply in the removal of the coarse scratches by the substitution of those which are finer and finer, until you can no longer see them with the naked eye. And even quite a while after, should the surface be subjected to a microscopic examination, it can be seen that the surface which did not appear to have any scratches is covered all over with an infinite number of them, all of which are so infinitesimal as to require a high magnifier for their discovery. A great care is absolutely essential to have the last polishing material uniformly fine, for if, by any mischance, a single grain of any coarse substance is mixed with it, visible scratches instead of a perfectly polished surface will be produced.