First of all, cleanliness should be observed. When there is dust or dirt about your room, particularly about the work-bench, failures will be frequent; for the smallest particles of rotten-stone, when allowed to come in contact with the buffs, will produce scratches on the surface of the plate, which very much injures the operation, and often causes failures.

Dust flying about the room is injurious, if allowed to fall on the plate, either before or after it has been coated, as it causes black spots which cannot be removed.

The polished plate should not be allowed to come in contact with a strong current of air, for it tends to oxidize the surface. Breathing on the surface should also be avoided, for the same reason.

The plate should, in all cases, be buffed immediately before using, and not allowed to stand any length of time. 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.