Why it's important
Just like anything in life it's important to know what you are buying. Jewellers often take for granted that their customers know the different types and don't take the time to explain. The financial implication can be big so here is a tiny overview of the basics.
The gold jewellery makers work with is combined with other metals to make it workable (an alloy). Gold in its purest form is too soft to work with. Think of gold leaf etc.
The amount of gold in those alloys varies and is described in carats. It refers to the proportion the gold accounts for (of 24 parts).
Typically in the UK jewellery is sold as either 9 carat or 18 carat. Increasingly you will also see 14 carat but this is more commonly seen in the USA.
18 carat has twice the amount of gold in it than 9 carat so will therefore command more than twice the price. Customers often ask which is better and it's not that 18 carat is necessarily better it is just more precious because it has more gold in it.
Advantages and disadvantages
18 carat has more gold in and so is softer and so more prone to scratches and so on. Personally I feel an amount of wear and tear is no bad thing it adds to the personality of a piece but if you want it to stay pristine for longer, go with a lower carat. It has a stronger yellower colour which many desire as it looks more like "gold".
9 carat gold is a great option if you want better durability and affordability. It is slightly less yellow in colour but still looks like gold of course! And the difference is less obvious when you're not comparing them next to one another.
When shopping for jewellery...
When you are shopping for jewellery retailers should clearly state firstly when an item is solid gold or gold plated. If it's gold plated then a 'layer' of gold is added to the outside of a piece of jewellery. The jewellery itself is normally silver underneath or even a base metal. It should state which. Gold plated jewellery is much more affordable because it isn't solid gold. If in doubt ask but if it looks to good to be true it probably is. There is nothing wrong with gold plated jewellery it offers the opportunity for piece of jewellery to look gold without the price tag BUT it will wear off. The piece will be hallmarked silver if it's made from silver.
If a piece of jewellery is solid gold it should be hallmarked with whichever carat gold it is. If buying online the description should clearly state what the carat is.
I try to make it clear on my own website in the title of a product and then in the "materials" section:
Almost all of my pieces are available in 9 carat or 18 carat. Sometimes 18 carat will be to order.
If I am working on a commission for you I will discuss carat options with you and more often than not provide a quote in both for transparency.