The local thickness of an electroplated nickel coating on a nonmagnetic base metal may be measured by the force of attraction of a small permanent magnet, the attractive force being determined with a simple spring balance. It was found that the attractive force between the magnet and coating is proportional to the thickness of the coating. The instrument is calibrated with nickel coatings of known thickness which have been deposited under about the same conditions as the coatings to be tested. Nickel coatings deposited under different conditions have somewhat different magnetic properties, which become uniform by heating the samples to 400 0 C (750 0 F). Specimens of unknown history should be annealed before testing. Measurements on coatings as deposited are correct within 15 percent and on annealed coatings within 10 percent.
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Abner Brenner (1937) studied this question.
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