Copper does not rust, but it stains easily and water makes black spots on it. Soot in moist air reacts with the metal to produce a green deposit called 'verdigris'. Clean off verdigris and dirt by rubbing hard with a paste of powdered chalk and methylated spirits on a soft cloth. Use a fine steel wool on stubborn areas, but beware not to scratch your antique piece in the process. The final stage of polishing is to use a metal polish - a soft cloth buffing wheel on a power tool gives a deep shine, but over large surfaces, polishing by hand with a soft cloth achieves a finer finish.
Clean a brass antique by washing it in detergent, then rubbing it with a solution of 1-heaped tablespoon of salt and 2 tablespoons of vinegar to a pint of water. Clean the old polish and dirt out of engraved brass with a solution of ammonia on a toothbrush, then with detergent and finally with clean water. Immerse badly corroded brass in a strong warm solution of washing soda for a hour, then wipe or brush the antique piece. If all the corrosion does not come off, repeat the process. Brush the stained parts with a glass brush, obtainable from a jewellers' supplier. Rub off spots of corrosion with scouring powder on a cloth or, if they are bad, with fine steel wool. Here, also, one should be very careful not to damage the antique with excessive rubbing. If scratches cannot be prevented then polish with a paste of whiting - a finely ground chalk obtainable at DIY shops. Dirty brass handles and fittings on antique furniture should, if possible, be removed before being cleaned. Otherwise, cleaning with polishes and lacquers will surely damage the wood.
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Metal polish, a soft cloth and hard rubbing produce the best results on both metals and of course, the likelihood of damaging your valuable antique this way will be significantly reduced. Delicate engravings might be rubbed away using metal polishes so in this case, vegetable oil on a cloth and some extra rubbing will be a better option to bring it to a shine. On deeply engraved antique pieces, use a medium-soft toothbrush to get metal polish into all parts, then with a soft brush inside a duster to get it out. Finish with a soft cloth.
There is no substitute for the sheen obtained on copper and brass antiques by regular polishing, but clear lacquer, obtained from DIY and art shops, saves much of the work. Because lacquer goes cloudy in cold weather and picks up dust in the atmosphere, it should be applied in a warm dust-free room. Spray or brush the lacquer on to the metal and, if it eventually starts to crack or break up - acetone will remove it. If an antique has been mended with soft solder, paint on a coloured lacquer to match or approximate to the true colour of the metal. Do not apply lacquer to a mended spot if the antique is 'raw', this will make a brighter patch that may not match the original sheen.
Dents in copper and brass antique pieces are best removed by pressing the metal against a short length of wood, shaped at one end to fit the curve of the damaged article. Press and rub against the shaped end until the dent is removed. Hammering is not advisable, although hammering with a 'planishing' hammer from the inside against a leather cushion is a professional method. Fractures in brass and copper antiques can be mended by soft soldering but cast brass is heavy and hard soldering or brazing makes a much better job of such joins.
Antique Copper And Brass Care CARE IMPROVEMENT