Many other types of nickel plating solution have been advocated, mostly based on nickel sulfate, although nickel chloride and nickel sulphamat bath can be worked more quickly. All these yield matt deposits and are called dull plating baths. The electroplated coating from the
The major modern change in the practice of nickel plating has been the use of brightening and leveling additions to the nickel plating solution of the
The operation and control of nickel plating calls for much care and experience. Temperature and clarity of solution, and the pH value must be constantly checked, e.g. twice daily; analysis for the main constituents, especially nickel is required at longer intervals. Nickel plating solutions are especially sensitive to trace contamination by trace of traces of copper, zinc and chromium, and by organic materials of a colloidal or glue like nature. The inorganic contaminants ca be eliminated by long continued plating onto a piece of scrap sheet metal at a low current density; organic materials are removed by oxidation with permanganate or by absorption on activated charcoal.
In addition to its use as undercoating to chromium, nickel plating is often used alone for protection of chemical plant and food processing equipment, or for parts, such as the electrodes of thermionic valves, which must be protected from scaling by the action of heat.
Thicker deposits of electrodeposited nickel are sometimes applied to worn or wrongly machined steel parts to restore them to size or make them oversize. In such cases great attention must be paid to the preliminary etching process, to ensure good adhesion, and to the mechanical properties of the electrodeposited coating. The deposit can be confined to specific areas of the steel part by applying a thick layer of adherent and chemically neutral wax to the remaining area. This is called stopping off and is also used to prevent unwanted plating on the shafts of suspension jigs, etc. in decorative plating.