The nickel baths for bright nickel to which brighteners, mainly bath-soluble organic compounds, are added, are mostly of the Watts type with widely varying proportions of chloride and sulfate. Boric acid is always present, usually not less than 35 g/l. Condition in the cathode film must be favorable not only for the deposition of nickel but also for the functioning of the brighteners function best at pH value of about 3 to 5 and bath temperatures of about 50 to 65oC.
The first brighteners of this class were the alkyl naphthalene sulfonic acids proposed. The commercial grades of these compounds were impure. The impurities resulted from the synthetic methods used in their large scale preparation, and materials as such caused brittle plate and were never used in practical nickel plating. These compounds were wetting agents and plates obtained were free from pitting. Benzene and naphthalene di- and trisulfonic acids was introduced without constituent groups, and these were successfully used commercially. They were far better than materials such as gum tragacanth and similar critical that only could be used for very thin deposits; otherwise the internal stress in the plate together with its brittleness would cause cracked, peeled plate. Sulfonic acids were not critical in concentration and did not caused poor adhesion or cracked plate with thick deposits; however, good brightness may be obtained on buffed surfaces and even then it left much to be desired. Unsaturated aliphatic sulfon compounds such as methyl, ethyl, propyl, or butyl or butyl sulfonic acids were developed.
The first brighteners of this class were the alkyl naphthalene sulfonic acids proposed. The commercial grades of these compounds were impure. The impurities resulted from the synthetic methods used in their large scale preparation, and materials as such caused brittle plate and were never used in practical nickel plating. These compounds were wetting agents and plates obtained were free from pitting. Benzene and naphthalene di- and trisulfonic acids was introduced without constituent groups, and these were successfully used commercially. They were far better than materials such as gum tragacanth and similar critical that only could be used for very thin deposits; otherwise the internal stress in the plate together with its brittleness would cause cracked, peeled plate. Sulfonic acids were not critical in concentration and did not caused poor adhesion or cracked plate with thick deposits; however, good brightness may be obtained on buffed surfaces and even then it left much to be desired. Unsaturated aliphatic sulfon compounds such as methyl, ethyl, propyl, or butyl or butyl sulfonic acids were developed.