Discolouration and natural aging of jewellery

Discolouration / blackening of the skin or clothes by items of jewellery causes doubts about the quality of the the piece.

The natural aging of a platinum ring

Knowledge as to why this happens should help to dispel fears and may even suggest simple solutions. This page attempts to explain how these effects may occur and how they can be overcome.

There are two main causes of this form of discolouration:

1. Metallic Abrasion

2. Corrosion

1. Metallic Abrasion

All metal can wear by:

1. Constant rubbing against itself i.e. links in a chain, swivels

2. Rubbing against other hard substances i.e. talc – a very hard, fine powder

3. Day-to-day chores such as driving, cleaning, lifting, washing-up etc.

The jewellery is not abraded by rubbing against the skin or clothing as neither is harder than the metal. However, the skin and clothes can carry hard particles from cosmetics, face and body powders, stiffeners/fillers in modern textiles, talc etc. The particles abraded from the chain appear black because they are so finely divided, and a small amount of abraded metal creates a large amount of dust. When this dust is in contact with absorbent or slightly greasy surfaces it can stick and form a black mark.

This can be reduced by:

1. Removing the causes – avoid harsh, textured cosmetic, do not talc areas where jewellery is worn

2. Harden the surface of the jewellery by good rhodium plating

2. Corrosion

The tarnished silver can be
seen on the inside of the ring

Pure gold is resistant to most chemicals associated with human skin. However, pure is rarely used to manufacture jewellery as it is too soft. It is therefore alloyed with other elements to improve its wear-resistance. Lower carat jewellery has higher additions of other elements. These alloys are no longer completely corrosion resistant and can be superficially attacked by a range of relatively mild chemicals.

2 a. Tarnishing

Tarnishing occurs under dry conditions i.e. in storage. it is caused by a reaction with sulphur compounds (particularly forming silver sulphide) and can generate a thin brown tarnish film and if not cleaned off prior to wearing, this will rub off on the skin.

This can be reduced by cleaning after storage and before wearing by rubbing with a soft cloth. If this is insufficient, cleaning with a proprietary cleaner may be necessary (i.e. detergent, Goddards cleansers or Silvo etc.)

2 b. Corrosion by the skin

Corrosion also occurs in the presence of weaker chemicals when aided by moisture i.e. sweat. Sweat is mainly water but also contains sodium chloride (salt), ammonia, urea, fatty acids and fat. It may also contain traces of other elements (particularly sulphur compounds and others associated with medications). These essentially mild chemicals when combined with moisture and a slightly elevated temperature (body temperature) can combine to cause surface corrosion on any jewellery in contact with the skin.

The typical mildly acidic nature of carrier alcohols in perfumes can also speed up this process. This can be reduced by:

• Frequent cleaning of jewellery, especially if it is exposed to perspiration, cosmetic and perfumes.

• Plating of lower carat jewellery to prevent even superficial corrosion