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Silver mug showing colour variation through polishing, about 1667-68. Museum no. M.150-1940

Silver mug showing colour variation through polishing, about 1667-68. Museum no. M.150-1940

Once you have thoroughly examined your object and identified any potential problem areas, prepare your piece for basic cleaning using the following guidelines:

Cleaning basics

  • Metals and their surface finishes are softer, more porous and more easily damaged than is often imagined. Inappropriate or excessive cleaning is a common mistake. When it comes to cleaning metals, less is more. 
  • Work on a padded surface (for example thin foam or cardboard covered with blotting paper) with good lighting.
  • If in any doubt, do not attempt any cleaning and seek advice from a conservator.

There is a difference between removing dirt and dust (cleaning) and removing tarnish (polishing). Polishing uses abrasives, so every time tarnish forms and is polished away, part of the original surface is lost. Repeated polishing may eventually lead to the loss of decorative details, plating, chasing, filigree work or even hallmarks.

The ideal treatment is to remove unwanted tarnish or corrosion and then maintain the object in that state. This may mean using an anti-tarnish product. Polishing typically produces shiny, reflective surfaces. It is almost impossible to remove dark patches or polish one area to match an adjacent lighter area. If you wish to try to leave some tarnish behind (for example, in the recesses in order to retain the patina of age), work over the surface as a whole, stop regularly to rinse off polishing residues and check that the surface has an even appearance.

Cleaning tools

The following tools are essential for safe cleaning:

  • Artist's sable brushes for dusting - tape over the ferrule (metal band between hairs and handle) with masking tape to prevent scratching.
  • Soft cloth

Taking things apart for cleaning

Metal objects are often constructed in several parts that are screwed or bolted together. Occasionally it is better to remove parts, for example wooden knobs from a metal object, before cleaning. However, dismantling can be problematic. Some metal items are assembled under tension, so when a screw is removed the pieces spring apart and are difficult to reassemble. Sometimes so much tension was used that it caused stress in the metal, which can fracture as you try to reassemble it.

If you decide to dismantle, make a careful note of where each part comes from - screws should be returned to their original holes, for example. You may need to label each component, and use a drawing or photo of the object to identify each part. Use good quality tools that match the job, for example screwdrivers should fit the slot snugly, otherwise the screw heads and the object itself can be damaged. Use masking tape on all parts of the tool that either come into contact with the object, or that might inadvertently scratch the surface of your object, for example, the metal ferrules on brushes.

Traditional or home remedies - to be avoided!

Traditional or home remedies usually rely on harsh abrasives, acids or alkalis to attack tarnish and should be avoided. The use of cola, baking soda, false teeth cleaner or lemon juice is aggressive and uncontrolled. The effect - a bright and shiny 'as new' appearance - is not usually appropriate or desirable. Traditional remedies are used for a 'quick fix' - the opposite of conservation, which requires a slower, more cautious approach and regular progress checks.

  • Ammonia - also known as ammonium hydroxide, ammonia will cause irreversible damage to many materials. Cast brass or bronze (both alloys of copper) are porous and the longer the contact with an ammonia solution, the greater the danger of deep penetration of both water and ammonia into the body of the metal. In some cases ammonia may leave the surface with an undesirable pink hue. Surfaces newly cleaned with ammonia tend to tarnish rapidly and thus soon lose their brightness.  The risks associated with the use of ammonia far outweigh potential benefits for cleaning

  • Commercial polishing products - avoid any such products which have a chemical action. Any chemicals which can strip metal corrosion products from a surface are also capable of attacking the metal itself sometimes leading to the loss of the more reactive metals from the surface of the alloy. When using commercial brands, less is more. It is important to remove all residues of cleaning product from the object's surface. Manufacturers can also change the formulations of their products without warning. Always check first that the product does not contain ammonia and if in doubt contact a conservator.
  • Water - avoid immersing metal pieces in water. Cast metal tends to be porous - there are often micro-voids in the surface that can trap water or other liquids. Some objects may have gaps in the solder which will also trap liquids. Water and other liquids may cause corrosion in the long term.

General care guidelines for objects in regular use

Metal objects in regular use, such as copper pans, silver flatware or teapots, pewter mugs and plates etc will benefit from these basic care procedures:

  • Make sure the objects are in good condition, without cracks or soft-solder repairs at the joints.
  • Clean as soon as possible after use - particularly after contact with garlic, fruit juices, eggs, salt or onions.
  • Avoid soaking, simply wash with warm, soapy water, and rinse thoroughly.  Never use a dishwasher.
  • Dry thoroughly with a soft lint-free cloth.
  • Store in tarnish inhibiting bags in a dry place.
  • Avoid storage with newspaper or rubber bands.

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