Cleaning Copper and Brass.
It is scarcely necessary to warn the collector against over cleaning, for to rub light bronzes which age has toned or encrusted with a beautiful patina would be vandalism indeed. Yet there are many objects which require attention when they arrive from the auction mart or curio-shop. Ancient bronzes should be washed in soap and water with soft brush or flannel—not scrubbed—and then dried in hot sawdust. If any polishing is necessary, a chamois leather or an old silk handkerchief will be sufficient. The green patina or verdigris of antique metals should not be removed nor its colouring spoiled with cleaning.
Copper vessels, however, do very frequently require cleaning. When they have turned a bluish green—not the much admired patina—they may be cleaned by making a paste of well powdered chalk and methylated spirit. This preparation should be rubbed on and then left until the spirit has evaporated and the chalk is quite dry, at which stage it can be removed and the copper polished with crocus powder or fine chalk.
Owing to long neglect there are some metal curios which cannot be thoroughly cleansed without a powerful solvent. A weak solution of oxalic acid may be safely applied with a piece of woollen material; it will remove the tarnish, and then, after well washing, the metal can be polished with fine chalk or whiting. When the brass is spotted with damp but not too deeply marked, chalk and spirits of turpentine will generally effect the purpose just as well.
Another recipe formerly much favoured by housewives in the days when copper vessels were much in evidence, is to rub them over with half a lemon dipped in salt; then after washing polish with a soft cloth. This is a useful recipe in that it does not injure an antique appearance or patina, but it will remove stains.
A somewhat more powerful preparation for metal-work is a cleaning paste made as follows: oxalic acid, 1 oz.; rotten stone, 6 oz; gum arabic, ½ oz.; sweet oil, 1 oz.; and then add as much water as necessary.
The following recipe is given for the benefit of advanced collectors who wish to avail themselves of modern methods. Such will no doubt delight in experimenting on the cleansing of newly acquired curios with a cleaning preparation operated by an electric current. Caustic soda, ½ lb.; sal soda, ½ lb.; resin, ¼ oz.; and water, 1 gallon; 4 to 8 volts and a current density of 12 amps. The greater the density of the current the quicker the cleaning is performed. A temperature of 120 Fahr. is recommended.