The floating particles of rotten-stone, after four minutes' subsiding, will be found fine enough for the finest Daguerreotype polishing required.
A quantity of such washings may be collected in a large bottle, and allowed to stand a few hours, when all the rotten-stone will have settled.

The water may be poured off and the rotten-stone put into an evaporating dish, and while being dried, must be constantly stirred to obtain an impalpable powder.
Further washings may in like manner be resorted to for finer qualities of rotten-stone.

In my practice, I have used the articles at two and four minutes' settling, and occasionally have prepared it after standing for eight minutes.

So fine a quality as this, however, is seldom required.

In using, rotten-stone, I mix with it, for polishing, fine olive oil, until I obtain a thin paste--and the best of all methods for polishing (well planished) Daguerreotype plates, is one like that used for glass by lens polishers; that is, by using a disc or buff-wheel, and having, a suitable holder by which to secure the plate, and then by pressing the plate against the revolving buff, well saturated with the mixed oil and rotten-stone, a very good surface is obtained.