The article to be blacked must first be well cleansed from grease, and then dipped into a solution consisting of 1 part of bismuth chloride, 2 parts of mercury bichloride, 1 part of copper chloride, 6 parts of hydrochloric acid, 5 parts of alcohol, and 50 parts of water. When dry, place the article in boiling water for half an hour. If the black is not intense enough, repeat the dipping operation. The colour is fixed by placing the article for a few moments in a bath of boiling oil, the article being afterwards heated until all the oil is driven off. This treatment is said to give an intense black finish.