18 karat gold

18 karat gold is a relatively high purity of gold (75% pure), used typically for jewellery purposes. Pure gold is naturally soft and for virtually all practical applications, gold must be mixed or alloyed with other harder metals. Therefore, most items referred to as gold are not pure but are in fact gold alloys, and 18 karat gold is one such alloy. Because of the high cost of gold it is important to know what proportion of precious metal has been used.

There are two commonly accepted units that measure gold purity. They are carat, or karat in the US - and the international millesimal system, or fineness.

Carat measures purity in parts of 24. In the UK it is spelt carat, and in the US 'karat'. 18 karat in the US is 18 parts of gold to six parts of other metals.

Fineness measures the gold content in parts of a thousand - making 999.999 pure gold. 18-carat gold then is equal to 750 fineness, or 75% gold.

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Carat and equivalent fineness

Karats	Parts of Gold	Purity (%)	Millesimal Fineness
24K	24/24	99.9	999
22K	22/24	91.7	916/917
18K	18/24	75	750
14K	14/24	58.3	583/585
12K	12/24	50	500
10K	10/24	41.7	416/417
9K	9/24	37.5	375

18 karat gold is still relatively soft due to its high purity, but is still suitable for jewellery that will not be worn every day, like gold bracelets. It is also a good choice for items like necklaces and earrings, that are not exposed to knocks and bumps.

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Is 18 karat gold valuable?

9, 10, 18 and 22-carat gold are most commonly used in the UK. 24 karat gold is used only as raw material or for bullion investment, as it is far too soft for wearable jewellery. 18 karat gold is then the third-most valuable gold alloy typically used in the UK.

The gold price of 18 karat jewellery depends ultimately on the gold market’s spot price. Working out the current value of 18 karat gold is fortunately very simple. By multiplying the current spot price by 0.75, you will get a rough 18 karat gold price. It should be noted however that the cost to refine and process 18 karat gold means you will usually get a price below this calculation.

BullionByPost purchases 18 karat gold at competitive prices. View our live 18 karat scrap gold price for a quote today.

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18 carat gold marking

The UK has a long history of legally requiring hallmarks on gold items. Currently all UK gold items weighing over one gram must be hallmarked. There are three compulsory marks; the maker or importer’s mark, the assay office mark and the gold purity.

The purity is shown in fineness. Traditionally the gold mark is contained in an eight-sided shape. The UK also recognises international convention marks. These are contained in two circles with weighing scales, and for 18 karat gold would look as shown below.

The US marking system is less restrictive; only a maker's mark is compulsory. The Federal Trade Commission does however advise that US jewellery should show a purity mark. 750 fineness is therefore often indicated simply by the letters 18k.

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18 carat gold colours

The metals used in gold alloys change its gold colour or tint. Because of its high gold content 18-carat gold is almost always bright and yellow - it can though be made in a huge range of tints. The three major shades are yellow, white and rose.

Yellow gold is alloyed with silver and copper or zinc. Rose gold is made by alloying with more copper than silver. White gold is alloyed with silver or platinum. White gold is also made by rhodium plating, this gives it an extremely hard finish.

• 18 karat is 750 fineness
• 18 karat gold is used in high value jewellery
• 18k gold will not withstand extremely heavy use
• 18 karat is made in a range of shades