Gold Purity
When people talk about gold, they often describe it in terms of karats (kt). An affordable piece of gold jewelry might be 10 or 14 karat whereas the more expensive pieces you can buy could well be 18 or even 22 karat. What exactly do these numbers mean?
What Are Karats?
Karats are a measure of purity - not weight. A small pure gold ring will thus have a higher karat value than a large brick of impure gold.100% pure gold is defined as having a purity of 24 karats. So if something is 24 karat gold then it's made of gold and nothing else - regardless of size. That is, as you'd expect, very rare except in the case of extremely thin coatings. Most gold items you buy in the stores will have a karat rating in the range 9 to 18. For example a 12 karat gold chain will be made from a blend of half gold, half some other metal such as copper.
So, if you're a rich celebrity you'll always choose to buy 24 karat gold jewery, yes? Probably not. Gold is a relatively soft metal and high-karat stuff tends to be easily damaged. A 24 karat item would more likely be reserved for display or ceremonial use. In the real world 18 karat is the highest level of purity usually worn. In the US the minumum karat value for an item to be sold as gold jewelry is 10. Here in the UK 9 karat is more common.
Why 24?
Why on earth did they choose a strange number like 24 to represent pure gold? Why not 10? Or 100 as in 100%?One theory is that the reason is mathematical. 24 divides evenly by 2,3,4,6 8 and 12. Thus it's easy to talk about a gold item being half pure (12 kt), two thirds pure (16kt) etc. Nine karat would thus be three eights gold, 18 karat would be six eights.