If the copper article is small the silver may be stripped by immersion in hot concentrated sulphuric acid, to which nitrate of potash crystals must be added in small quantities as the work proceeds. The acid must be kept, hot in a porcelain or vitrified stoneware vessel. The article to be stripped must be dry and free from grease, lacquer, or varnish. It must be gently moved whilst in the acid and closely watched, and must be taken out and rinsed in clean water when the silver has been removed; the acid will then not deeply corrode the copper, which may then be polished in the usual manner. If the articles are too large to be thus treated the silver must be rubbed off in the process of polishing. Silver may be stripped from other metals by electrolytic action in a bath of potassium cyanide, with the article connected to the positive pole of a battery or dynamo, and a small silver plate connected to the negative pole. The article must be removed as soon as all the silver is dissolved.