Improvements in methods for stripping coatings from coated metal articles

Abstract

Abstract In a method of stripping a composite coating formed of a plurality of layers of different metals from a metal article where the outer layer consists of or comprises one or more metals of the platinum group and the undercoating is of base metal, the coated article is treated with a solvent that will dissolve the base metal but will not attack the metal of the article or of the outer coating layer. In stripping a composite coating of a plurality of layers of nickel and rhodium from a silver or silver-plated article, the article is immersed in an acid bath, e.g. one comprising a mixture of phosphoric and/or hydrochloric acid and water, the major portion being the acid, which dissolves the nickel but does not attack the silver. The phosphoric &c. acid may be replaced by an organic acid which does not attack silver such as acetic acid, and the bath may also contain a small quantity of a metal sulphate such as aluminium sulphate and also sodium chloride. In one example, the bath comprises a mixture of two-thirds of a litre of phosphoric acid and one-third of a litre of water containing 56 grams each of aluminium sulphate and sodium chloride. If desired, one-third of a litre of phosphoric acid may be substituted by one-third of a litre of hydrochloric acid, and the amounts of the sulphate and chloride are 28-56 grams.

Inventors

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