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• Carat is the measurement of purity in gold alloys and is shown in 24ths.
• Gold carat measurement is different to the carat measuremens used in gemstones and diamonds – click here to read more about gemstone quality.
• The carat rating is found by dividing the mass of pure gold (or platinum) in the alloy by the mass of the material being evaluated, this number is then multiplied by 24. -That is why 24 carat gold is the purest.
• A single carat is 1/24 purity by mass.
• 12 carat gold is 50% gold.
• A metric system has been introduced in the UK by which purity is represented in parts per thousand – 18 carats is therefore 750 parts per thousand.

Gold Alloying

Pure gold isn’t used in jewellery because it is so soft that it will break or bend easily unless handled very carefully or made thicker for strength. This is why film and TV characters often bite items of gold to check for purity. Other metals are used to strengthen the jewellery in a process called alloying.

Most gold jewellery is made using yellow gold alloys -that is, gold mixed with copper and silver. Silver, zinc, or palladium are used to produce white alloys, or “White Gold”.

Alloys can make many different colours of gold jewellery – in the UK, white and rose coloured gold are becoming increasingly popular, though optimum colours depend on your skin tone and wardrobe. In the UK, 9ct and 18ct is most commonly sold, while in America, 14ct is more popular. In India, 22ct gold is preferred. 24ct gold tends to be used for exchange and investment.

Platinum and White Gold

Platinum is different to white gold. Platinum is more expensive than white gold alloys and itself has a carat rating system for purity. It has to be heated to higher temperatures than pure gold in order to make jewellery and is quite difficult to work although it makes very good settings for diamonds. Platinum is a silvery grey colour unlike white gold which needs rhodium plating to achieve the optimum colour.

Rhodium plating is vulnerable to tarnishing – though H Samuel will re-rhodium plate any white gold jewellery within 12 months of purchase for free. Many people choose rhodium plating over platinum because it has a highly reflective white surface.

Hallmarking

British hallmarking was introduced over 600 years ago and was probably the first example of consumer protection law.

When you’re buying gold jewellery, make sure it has a hallmark. This is a quality control mark placed on gold, silver and platinum and provides a safeguard to purchasers. The hallmark on an article shows that it has been tested (assayed) by an independent body (the Assay Office) and guarantees that the metal is of one the legal standards of fineness, or purity. You therefore know exactly what you are buying.

Hallmarking is carried out in the UK not only by the London Assay Office, at Goldsmiths Hall, but also by the Birmingham, Edinburgh and Sheffield Assay Offices. These institutions are hundreds of years old and will also test for nickel and mercury.

A hallmark allows your jeweller to quickly identify what carat your jewellery is if you have to take it for repair or alterations. It is illegal for most articles of precious metal above a certain minimum weight to be described, or sold, as gold, silver or platinum, unless they carry an approved hallmark.

A British hallmark is made up of at least three compulsory symbols:

• The Sponsor’s Mark – This indicates the manufacturer, or sponsor of the item. This consists of the initials of the person or firm who sent in the item for assaying.
• The Fineness Mark – This indicates what the metal is and its standard of purity in parts per thousand.
• The Assay Office Mark – This identifies the Assay Office at which the item was tested and marked.

There are also optional marks:

• The Common Control Mark – This contains the standard of purity. The shape of the shield indicates what the metal is.
• The Pictorial Quality Symbol – This indicates the metal by picture.
• The Date Letter – This indicates which year the item was submitted for hallmarking. Since 1986, this has been an unnecessary feature on small items of jewellery.

Once upon a time, sterling silver was represented by a lion, but is now replaced by the numbers 925. To find out more about hallmarks since 1544, read “Antique Marks” (just click here) – an excellent work on the subject.

Caring for Gold Jewellery

Gold is very durable, but it can be damaged if not cared for properly. By following a few simple rules, your gold jewellery will stay beautiful.

• Gold can be scratched or dented if it’s treated roughly. Don’t wear your gold jewellery while doing heavy work, and avoid contact with gritty substances.
• Chlorine can attack the surface of gold and lead to damage. Take off your gold jewellery before entering a swimming pool.
• Store each item of jewellery separately to avoid scratches – see a selection of jewellery boxes here.
• Jewellery can best be kept clean by using a special cleaning solution or cloth. A variety of these, for different types of jewellery, are available here.
• Check your jewellery regularly for damage or weakness, paying particular attention to prongs, joints and fastenings.
• H Samuel offers a comprehensive repair service for most items of jewellery. All repairs are carried out by highly skilled craftsmen, and are guaranteed for 12 months.
• H Samuel will re-rhodium plate any white gold jewellery that was bought from them free of charge within 12 months, as long as you have proof of purchase.