Metals

Tin and its alloys

Tin is a soft, white metal which is found in essentially pure form in some objects such as plates; but it is more commonly seen alloyed with lead in the form of pewter.

In the 19th and 20th centuries, tin was combined with a number of other elements to produce a range of alloys which were used principally for utensils and ornamental ware.

Typical examples are:

• Britannia metal which is 93% tin, 5% antimony, 2% copper. It was developed in England during the mid-1700s in response to the threat to the pewter utensil industry from cheap porcelain. Old pewter was dull and, because of its lead content, was undesirable as a food container. Although the new alloy was brighter and stronger, it eventually lost favour as a metal for the production of household utensils; and

• leadless pewter which is alloyed tin.

Corrosion of tin

Although it is normally quite stable, tin reacts slowly with the atmosphere to form grey, stannous oxide and finally stable, white to grey-black stannic oxide.

Many museum objects made of tin or its alloys are covered with a dull, grey coating of corrosion products. These form a protective patina. Unless very pronounced or unsightly, this patina should be retained.

Cleaning tin

Although tin objects are quite strong, careless handling will still damage their surfaces.

If an object must be cleaned, a pure soap in warm water can be used to remove dirt and grime. This should be followed by rinsing it with fresh water, wiping it with methylated spirits and then polishing it with a soft cloth.

Ask the advice of a conservator before treating badly deteriorated objects.