Despite their apparent toughness, metals can scratch, dent or fracture, or may corrode. As always, care for the weakest material in an object. If possible, detach the metal parts and clean them separately.
General Metal Cleaning
Cover the working surface with a soft cloth, and wear cotton gloves, as fingerprints can leave deposits which cause tarnishing. Before cleaning, check for loose parts or splits in the metal.
Use proprietary metal polishes as little as possible, as they actually remove a small amount of metal. Regular dusting with a soft cloth, and a soft-bristled brush for awkward crevices, reduces the need for major cleaning. For grime or light tarnish, wash metals (not bronze or iron) in warm water with mild liquid detergent. Only immerse objects if they are all-metal with no weaker materials; cotton buds are useful for cleaning small areas. Rinse the articles and dry thoroughly with absorbent paper. Never put precious metal objects in a dishwasher as the salts and detergents may pit and stain the surface.
For heavier-duty cleaning on silver, brass and copper, you can use long-term metal polishes. They have an in-built tarnish inhibitor that reduces the need for frequent cleaning. First of all, use a soft brush to remove dust and dirt which could scratch the surface if rubbed in. Do not use wire wool or an abrasive cloth to dislodge stubborn stains. Apply the cleaner with a soft cloth or soft brush in a gentle circular movement. Immediate rinse and dry the item with an absorbent paper towel. Remove polish from crevices with a dry, soft brush.
Lacquer seals silver, copper and brass against corrosion. This not only deprives an object of a sometimes desirable patina, but the lacquer is easily scratched and marked by fingerprints, and can soon look patchy. A light coating of microcrystalline wax applied after cleaning is an effective and less radical barrier. Lacquer is worth considering for display items with intricate decoration which would wear away with too much cleaning.
Wrap silver in acid-free tissue or undyed cotton wool to reduce tarnishing. Sulphurous foods such as egg and Brussels sprouts cause tarnishing, so the sooner table silver is washed after contact with them, the better.
Tarnishing is not actually harmful to silver. Over-zealous cleaning however exposes the base metal core on a plated object.
Avoid using metal polishes on pieces that you wear, on clocks or watches (where they could damage the mechanism) or on niello work. Silver or jewellers’ cloths and silver dip (which can be wiped on large objects with cotton wool swabs) or foam, are the least abrasive cleaners. Limit the number of items treated per jar of dip, as particles of silver from cleaned objects can give an unsightly deposit that is difficult to remove.
Silver which contains a large proportion of copper may corrode if it has been in a damp atmosphere, causing a green crystalline deposit. Wipe off this verdigris off plated silver with methylated spirits. If it appears on solid silver, a metal conservator should chemically treat it.
You can resilver worn electroplate, either professionally or using a proprietary replating agent. There are possibilities that finish and colour may not be true to the original and the sharpness of any engraved decoration may dull. The process may well devalue an antique piece, particularly in the case of Old Sheffield plate.
Establish whether a gold object is solid or plated, silver gilt, or ormolu. Gold is soft, and the thinner the layer, the more easily it will be rubbed away. Gold also scratches easily, but does not tarnish unless it has high silver content (as in some 9-ct gold). Light dusting should be enough. You can wash gold objects as long as no weaker materials such as porous gemstones are present.
Copper and brass
The natural patina on brass and copper is a sought-after and valuable asset on some antique pieces (brass carriage clocks, for example), and such pieces should never be cleaned with metal polishes. Copper tarnishes to brown and corrodes to a relatively stable green patina; brass eventually acquires a matte, greenish-brown surface. Both metals scratch easily. Regular, light burnishing with a soft cloth or chamois should be adequate, or use a long-term silver cloth for light tarnishing. For heavier stains, use long-term brass and copper cleaners or impregnated wadding.
Pewter is easily dented and scratched. Old pewter has a high lead content which reacts and corrodes more quickly in acid conditions, so avoid keeping the metal in oak furniture, which is particularly acid, and always wrap in acid-free materials for long-term storage.
It’s debatable whether pewter should be allowed to develop a matte, tarnished surface or polished to a silvery finish. A dull gleam induced by regular, light buffing with a dry cloth is a good compromise. Try gently wiping a heavily stained or very dull surface with a rag impregnated with linseed oil and talcum powder. Remove this mixture using cotton-wool swabs moistened with methylated spirits, and then wash, rinse and dry thoroughly. A metal conservator should treat warty spots or powdery corrosion (caused by lead reacting with acids in the atmosphere).
Iron and steel
If exposed to damp, iron and steel rust rapidly, and will then pit, flake and eventually disintegrate completely. Cast iron and wrought iron can be given a barrier coating of paint or graphite, but overpainting the original finish can reduce value. A microcrystalline wax or light penetrating oil are also suitable for steel. Bear in mind that direct heat cracks paint, so iron grates and firebacks in use should be black leaded.
Before cleaning iron or steel, make sure the metal is absolutely dry. Remove loose rust and paint from tough objects with wire wool or a wire brush followed by a commercial rust remover or wire wool soaked in paraffin. Wipe clean and dry thoroughly, then coat with a rust inhibitor.
Remove minor rust spots with a mild abrasive cloth and a few drops of a light penetrating oil, or gently scrape them off with a scalpel. Methylated spirits or white spirit are also useful cleaning agents. Severe rusting needs professional treatment, such as sandblasting or chemical stripping to restore the surface to good metal.
With thanks to Readers Digest.