Pure gold is 24 carat (ct), very soft and bends easily. To make gold jewellery more practical and durable it is alloyed with other metals. Different alloys are used for greater strength, durability and colour range.
The caratage of the jewellery will tell you what percentage of gold it contains:
18ct (750) gold means 18 out of the 24 parts are gold (75%) and 6 parts alloys. 14ct (585) gold means 14 out of the 24 parts are gold (58.5%) and 10 parts alloys
9ct (375) gold means 9 out of the 24 parts are gold (38.5%) and 15 parts alloys
When comparing gold jewellery, the higher the caratage, the greater the value.
Gold Carat Marks
When buying gold jewellery, always look for the carat mark. All other things being equal, the higher the carat, the more expensive the piece. 18-carat gold is 18/24ths, or three-quarters pure gold, and jewellery of this fineness is marked 18k or 750, the European designation meaning 75% gold. Always look for the carat number or carat mark, “750”, “585”, “375”,”k” or “ct” that must appear on the piece. The heavier the piece, the more gold it contains.
Yellow gold is alloyed with silver and copper. It is the most frequently used type of gold there is. Malleable, ductile, and generally non-corrosive, it has a high melting point and is not susceptible to compression.
Rose (red) gold is alloyed with copper, and perhaps silver. The proportions are about one part of copper to three parts of 24-karat gold.
White gold is alloyed with silver and a selection of other white metals. The percentage of gold naturally varies, according to the amount of other metal used. White gold is highly reflective and not subject to tarnish. The ancient term for it was Electrum. Its use predates that of Palladium and Platinum.
Why does white gold change colour?
“White gold” is a misnomer, gold is actually yellow in colour. In order to obtain a white or grey colour, other metals such as nickel, silver and palladium are added to bleach the yellow gold to a white colour. Rhodium is then plated on the jewellery to give the very bright white finish. The amount of the bleaching metals vary according to health requirements, method of manufacture and cost of manufacture.
Nickle is an effective bleaching metal, but only relatively small amounts may be used with gold. A large number of people develop an allergic reaction (excema) if the nickle content is too high. The nickel alloys that are unlikely to cause the allergic reaction have a slight yellow tinge. The jewellery is therefore then plated for the bright white finish. The colour of the rhodium plated jewellery may change when the rhodium plating wears away.
Maintenance of your jewellery is important. When the bright white rhodium plating has worn off your jewellery, we can repolish the piece and rhodium plate it again.