The properties of precious metals

The Gold Myth

In New Zealand, there is a choice between 9,14 and 18 carat (ct) gold. It is a common misconception that 9ct gold is harder wearing than 14 or 18ct gold. 9ct has a Vickers hardness of 120 and 18ct has a Vickers hardness of 125. While this shows that 18ct is harder, in practical terms 9ct and 18ct are much the same. 9ct is however, more difficult to bend and is a little springier than 18ct. Therefore a thin 9ct ring may be less likely to bend out of shape than a thin 18ct ring. This is why a lot of the lightweight and cheap jewellery is manufactured in 9ct gold. However, if your jewellery is of good sturdy construction, neither metal will be likely to bend out of shape. The gold content in 9ct gold is very little, it has more parts copper and silver than actual gold. See the table below to see a typical gold alloy recipe.

The colour of gold

The difference in colour between yellow, white and rose gold is determined by the metals used in the alloy mix. The colour of any gold alloy will not chip, fade or wear off with age.

Yellow Gold

Yellow Gold is an alloy of pure gold with metals such as copper and zinc. In yellow gold the copper content determines the colour of the alloy. For instance, 24ct is pure gold, whereas 18ct gold has 18 parts of pure gold and 6 parts of copper and zinc; therefore 9ct gold only has 9 parts pure gold content and the rest (15 parts) copper and zinc.

Rose gold

Rose gold has a higher copper content than yellow gold, giving it a rose-reddish colour.

White gold

White gold is an alloy of pure gold and white metals such as silver and palladium. Often, white gold jewellery is plated with Rhodium.

Silver

Silver is quite soft and not as durable as other metals, the advantage however, is the price, when compared to gold, platinum etc. Silver will tarnish, requiring regular cleaning. Some people may experience skin reactions to silver.

Rhodium

Rhodium has similar properties to platinum. It is used predominately for plating, (mainly white gold jewellery). The natural colour of white gold is actually a light grey but rhodium plating gives the gold a whiter and brighter appearance. Rhodium plate is only a thin surface coating and will wear off eventually, however it can be re-applied in most cases.

Platinum

Platinum is a white metal, but unlike gold it is used in jewellery in almost its pure form (approximately 95% pure). Platinum is extremely durable, and retains it’s brightness, so it does not need to be rhodium plated. Platinum is very dense metal, so a platinum ring will feel heavier than an 18ct gold ring. Platinum is, however, significantly more expensive than gold. As a rough guide, a platinum ring will be approximately twice the price of an 18ct white gold ring.

Palladium

Palladium is a relatively new metal to the NZ jeweller but it has been used in Jewellery worldwide since 1939. It's natural colour properties mean that it doesn't need any plating to enhance its white appearance. It has been used as an alloy for making white gold for many years. As a PGM (a platinum group metal) it is a great alternative to white gold and with a lighter specific weight than platinum - it is an affordable option.

Titanium

Titanium is a natural element, which has a silver-greyish colour. Titanium is the hardest natural metal in the world and yet is very lightweight. Pure titanium is also 100% hypoallergenic, which means that it is safe for anyone to wear, and will not cause skin reactions. Titanium is very strong, giving it more dent, bend and scratch resistance than gold, silver and platinum. One factor to consider with titanium is that it cannot be soldered. This limits the design of your jewellery and also means that titanium rings cannot normally be resized.