When you're buying a special piece of jewellery - whether it's an engagement ring or a birthday necklace - it's likely you'll hear the term 'precious metal' thrown around a lot. But what exactly is a precious metal - and what makes it so 'precious'? When it comes to jewellery, the three most precious metals are silver, gold and platinum - in that particular order. And if you're buying jewellery made out of these metals, it's important to know what each of them denotes, and how expensive they are, before making your purchase.

Silver, for example, is one of the cheapest precious metals, and currently sits at about one fiftieth the price of gold by mass, although it did once trade at one sixth the price of gold before the Age of Discovery. As a soft metal, silver needs to be alloyed with other metals before being made into jewellery, in order to make the metal stronger and more resistant. 'Sterling Silver' needs to contain at least 92.5% pure silver in order to gain this mark (the remaining 7.5% is usually comprised of copper). This small copper content means that silver jewellery is likely to tarnish, so if you're thinking about buying a sterling silver ring or bracelet, it's important to make sure you clean in properly. Many people like to use toothpaste to clean silver jewellery, but if you're looking for a less abrasive cleaning formula, it's best to invest in a silver-cleaning fluid at the time of purchase. Further, to make sure the silver jewellery you've bought is high quality, ensure that it's been stamped with a purity mark (like 925) before you buy.

Gold, on the other hand, has long-held associations with investment and wealth as a precious metal. As with silver, gold is a soft metal and so also has to be alloyed with other metals to make it hard enough for jewellery making. Pure gold, for example is yellow, while white gold is gold that has been alloyed with nickel, copper and zinc, and can sometimes look similar to platinum. In this way, the colour of gold can be manipulated in order to create a number of different types.

Of these three popular precious metals, however, platinum is the most expensive. Its heavy-weight and durable nature means that it's great for diamond-encrusted jewellery and is similar in colour, though not in properties, to white gold. Generally speaking, is 90% pure platinum and 10% iridium or palladium alloy. Moreover, jewellery that contains more than 95 per cent pure platinum is marked 'platinum' (950 plat or 950pt), whereas 85 percent pure platinum will be marked 850plat or 850pt. Platinum jewellery is rapidly gaining popularity and other related metals - like palladium and titanium - are, as a result being used with increasing frequency in jewellery-making. Hence, platinum jewellery designs are often modern and chunky, with an ethos that reflects the lifestyle of its new buyers.