The Facts: 9ct vs 18ct

by Kate Reid
November 2, 2018 / Jewellery Buying Guide,Learn About Metals

When choosing a piece of fine jewellery, whether ready-made or custom-made, there is a long list of things to consider. It is a good idea to write some of the key points down and work out what is at the top of the priority list and what is down the bottom.
One important decision is which metal you should choose? This often leads to the question; should I save some money and go with 9ct gold or invest a little more and choose 18ct gold? You may be wondering what exactly the ‘ct’, sometimes seen as ‘K’, refers to. The ‘carat’ of a metal denotes the percentage of pure gold in the alloy, with 9ct being 37.5% and 18ct 75% pure gold. Many come in and ask if it is true that 9ct gold is harder than 18ct gold. This is a misconception. In the case of white gold, the reverse is true, 18ct white cold in considerably harder than 9ct white gold. In yellow and rose golds, the hardness between the two is virtually the same. Gold, in its pure form, is one of the least reactive elements so 9ct gold, having been mixed with a higher percentage of other elements, therefore, is less resistant to exposure to chemicals, such as chlorine for example. Exposure to chemicals and perspiration can mean your 9ct jewellery may appear dull and discoloured. At the end of the day, though more expensive, 18ct gold has twice the gold content of 9ct making it superior in terms of durability and performance.
This does not mean that 9ct is not a fine choice for certain jewellery. In fact, 9ct can be a great choice for dress rings, earring and pendants that are not worn every day. For pieces such as engagement rings, which are made for everyday wear, 18ct is a much more durable and long-lasting choice.
It is also important to outline the difference between 18ct white gold and platinum when discussing which metals are more suitable for certain designs. Platinum is a white metal that is used in its almost pure form (95%). It is also extremely dense making it heavier than white gold. Platinum is renowned for its hard and longwearing qualities, which is what makes it so ideal for engagement rings with very fine settings. The other bonus about Platinum is that because it is white in its natural state there is no need to have it rhodium plated as is the case with white gold. What is the catch? Platinum is quite expensive, around double the cost of 18ct gold depending on current metal prices.

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