by Tim Harry

Created on: July 20, 2009   Last Updated: February 11, 2012

It is a question that many people will ask hoping for a sensible answer, what is the difference between 9 and 18 carat gold?

Men in particular often seem confused between the different grades of gold, and whilst they will recognise that 18 carat gold is more expensive than 9 carat, the actual difference is a mystery. Most people will simply accept that the greater the carat value the better the gold or the piece of jewellery made from it. There is though a lot more to carats of gold than just a number.

Of course there is a need for a basic understanding of what the word carat actually means. In relations to gold and some other precious metals, carat, or karat, is a measure of the purity of the item, with 24K being pure and anything lower than 24K less than pure. The purity is simply worked out by dividing the mass of gold in an item by the total mass of the item. Thus a scale is achieved where 12K gold is made up of fifty percent of the previous metal, and fifty percent of some other metal or metals. Thus on the carat scale, 18 carat gold is 75% pure gold, or 750 parts gold, whilst 9 carat gold is 37.5% gold, or 375 parts gold.

So the basic difference between 9 carat and 18 carat gold is the amount of gold in the item. This also means of course that there are different proportions of other metals in the items. Many people will say that 18 carat gold is always harder than 9 carat gold, and although this is generally true it does depend on the alloy formed. It is also true though that 18 carat gold is harder than 24 carat gold because of the other metals added to ensure that the gold can be worked and will not be destroyed with normal wear and tear. Also 9 carat gold is less resistant to chemicals than 18 carat gold.

The majority of metals used in the gold alloy are going to be cheaper than gold, thus the logical reduction in price the lower down the carat scale a piece of gold is.

The different gold alloys have a different colour, and as the range in colour of gold can range from the traditional deep yellow through to pale yellow, but also includes greens and reds, it is important to know the metal content. These colour changes though cannot always be used to determine the difference between 9 carat and 18 carat gold as similar results can be achieved with varying the metals involved.

In essence though, with the addition of silver to gold, the new alloy will be coloured somewhere between green-yellow and white. Copper makes gold appear redder. Nickel is a cheaper version of silver and will make gold appear whiter, and zinc is used to offset the impact of copper, making a reddish gold return to a yellow state.

There are drawbacks in buying 9 carat gold compared to 18 carat gold, and this is perhaps only logical otherwise everyone would buy the cheaper option. Nine carat gold will normally have a large amount of copper in it. Copper reacts with the atmosphere and as well as causing the gold item to tarnish and sometimes turn black, will also normally result in green marks being left on clothes and skin. Some countries also have a preference for using nickel in their gold alloys, and this is why many people believe that they are allergic to gold. They probably aren't and are probably just allergic to nickel, which will cause a rash on the skin.

As with most things always buy the best that you can afford. Eighteen carat is better than 9 carat, just as 20, 22 or 24 carat gold are better than 18 carat.

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