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. A quantity of plates may be prepared in this way, and all
the adhering oil, etc., may be removed by a clean hand, or lathe buff,
after which each plate must be heated to the point necessary to burn
off the remaining oil great care being required not to overheat the
plate. A very slight excess of temperature will at once destroy all
the polish previously obtained. The test for ascertaining the right
temperature is at hand; the adhering oil will be driven from the plate
in the form of smoke when the right temperature is reached. The moment
the smoke ceases to rise from the plate, the heat must be removed, and
the plate quickly cooled upon a piece of iron.

A quantity of plates thus prepared may be kept on hand for any required
time, and the labor of one minute, with a lathe or hand-buff with dry
charcoal, or rather, prepared lampblack, will perfectly polish the
surface ready for indexing, etc. This lampblack also requires some
care in preparing. Take a small-size crucible, properly temper it by a
slow fire, that it may not be cracked after which, fill it with common
lampblack, cover it over with a piece of soap-stone, and again replace
it in the fire. Build a good hard coal fire around it continue the
heat for two or three hours, being careful not to raise the cover till
the crucible be quite cold. Pulverize when using it. It is very
desirable to keep this lampblack dry and warm. Some operators use much
rouge I would recommend the above in preference; but those who feel
that they cannot dispense with the use of rouge, had better try a large
addition of prepared lampblack to a small one of rouge, as this latter
article, unless great pains be taken in its preparation, will adhere
and work itself into the body of the surface, so that it cannot be
removed th