Could anyone care to explain how exactly gold is measured and what are the criterion that make gold better quality?

In order for a gold jewelry to be called 'pure' it has to expectedly contain 24 karats of gold - as this is the highest possible quality. However, in order for a gold jewelry to be called 'solid' the gold jewelry has to contain at least 10 karats, which in terms of percentages means at least 41.7% presence of gold in the alloy, which is in fact even less than half!

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First of all, the measurement term used with gold is called a karat, not to be confused with a diamond's carat, which is spelled differently (although when referring to gold's karat, it is frequently also written as 'carat' and then it gets a bit confusing). When preparing gold jewelry, the pure element gold is often mixed with other, less precious metals, in which case the mixture is referred to as an alloy – a mixture of different substances. Karat is actually a measurement of the purity of the gold element inside an alloy, and therefore always has a corresponding percentage value in relation to the whole alloy. The actual measurement is calculated with the help of an equation that is based on the fact that one carat is 1/24 purity by mass. In simple terms, this means that the best quality gold you could find will be a 24 karat gold, because this means it has 99.9% of the gold element inside the alloy. So in fact it's quite simple: the less percentage of Au (Au is the chemical element gold) that is found in the alloy, the less karat value received, and therefore the worse the quality gets.

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