general are dust, rouge, or a spray of moisture on the plate.
It this be the case, there is no solution which can remove them,
as they have prevented a chemical action with the silver,
and their removal would only expose the surface of the plate
which in itself would afford a contrast with the impression.
Another and less dangerous source of these specks is organic matter
contained in the solution employed in dissolving the chemicals,
or the water in washing. much of the hyposulphite of soda
in market contains a sulphuret, which, coming in contact
with the silver surface, immediately causes oxidation.
Such spots, as well also as most all others found on the plate
after it has been exposed in the camera, can be removed
by the following, solution: To one ounce of water add a piece
of cyanide of potassium the size of a pea; filter the solution
and apply by pouring it on the surface of the plate.
In all cases the plate should first be wet with water.
Apply a gentle heat, and soon the spots disappear,
leaving the impression clear and free from all organic matter.

In the absence of cyanide of potassium, a solution of pure hyposulphite
of soda will answer as a fair substitute.

To Redeem, a Solarized Impression.--The Daguerreotype plate,
prepared in the ordinary manner, should be exposed in the camera
a sufficient time to solarize the impression. Then, before it
be exposed to the vapor of mercury, expose it for a very brief
period to the vapor of either chlorine, bromine or iodine.
Then expose over mercury, as usual. I have produced singularly
interesting results by this process.