It should be held with the polished face downward.
It is always best that the plate should be of the same temperature of the atmosphere in the room.
Keep the camera and mercury-bath perfectly free from the vapors of iodine and bromine; for the presence of the slightest degree of either of the above will injure the impression in no small degree.

As a preventive, let the camera be exposed to the sun or fire for a few minutes in the morning.
Filter your mercury often, to keep the surface free from film and dust.
The hyposulphite solution should be filtered through sponge every time it is used.
The direct rays of light must not enter the camera in conjunction with those reflected from the object; or the picture will be veiled, and the color of the plate changed to a thick green.
If the plate be iodized only to a light-yellow, the result might be of a bluish or grey tinge: and this is generally the case, when the quick is new and strong, and there is an excess of it on the plate, and yet not enough to form the bromide iodide of silver; in which case it would wholly spoil the impression.
Your iodine will be found to operate more successfully, when the time required for coating the plate does not fall short of fifteen seconds, or exceed one minute.
Too quick coating can be avoided by using less iodine in your box.

In the summer months, when the weather is 80 deg.

and over, one quarter of an ounce, or even less, will work to advantage.
ELECTROTYPING.
I am indebted to Mr.J.H.Fitzgibbons for the following process, which he employed in producing the excellent specimens he exhibited at the Crystal Palace: "I shall endeavor to lay down in as comprehensive a manner as possible the method by which I have been enabled to produce the most satisfactory results.

I use a Smee's battery (another kind will do).
After filling the cell, of common size, nearly full with water; add about quarter of an ounce of sulphuric acid.