The amount of surface used for amalgamating is determined to some extent by the process used for gold recovery. If the cyanide process follows the plates, it is necessary only to extract the gold not easily dissolved in cyanide, that is the coarse particles which may have been flattened and floated in the tube mill. If amalgamation is the sole method of gold recovery, the plate area must be such that all the gold is amalgamated.

Plates must be dressed whenever the surface shows any foulness, which may be twice a day or oftener, once to take of! the excess of amalgam and at other times to clean the surface. In tube mill amalgamation, when a plate is being cleaned, the pulp must be switched to another plate and the process conducted as in stamp mill amalgamation, except that the plate must be better protected with amalgam. If the cyanide process is used, the plates are kept wetter by reason of the greater amount of mercury used in the mill. The plate is sprinkled with mercury and well rubbed with a whisk broom. A rubber scraper is then used to gather the amalgam by first scraping down the sides, then toward the center and then toward the head of the plates where the amalgam is taken off in a scoop. The plate must not be robbed entirely but enough amalgam left to form a smooth plastic coating. Plates 16 ft. long may be cleaned and brushed at the rate of 7 min. a plate, but if the ore is particularly refractory the time required may be twice as great, as the plate will probably be covered with compounds which require careful removal.

If chemicals are used on plates, let it be sparingly for any ores that require chemicals to promote amalgamation contain substances that form compounds with the chemicals that prevent amalgamation.