18ct gold is 75% pure gold and 25% other metals (usually a combination of silver and copper). In the case of white gold, that 25% consists purely of white metals, present to contribute a silvery hue.
9ct gold, on the other hand, has a content of 37.5% pure gold and 62.5% other metals.
In short, 18ct gold is 18 parts pure gold; whilst 9ct gold is only 9 parts pure.
Carat weight is in fact the only factor to influence the appearance of gold. Whilst provenance makes no difference (Fairtrade, Fairmined, recycled or industry standard - 18ct gold looks like 18ct gold), the lower the gold content the more diluted the metal in hue. You'll notice that 9ct gold is lighter, less yellow and less lustrous than its 18ct counterpart.
All in all, 9ct gold is tough enough to survive a lifetime of wear - but 18ct gold is better suited to heirloom pieces chosen with future generations in mind.
Whilst 9ct gold is technically 'harder' than 18ct gold, scoring higher on the Mohs Scale of Hardness, this doesn't mean it's more resilient in the long-term. 9ct gold is in fact more brittle, which means it's less resistant to knocks and scratches on a microscopic scale. When compared over a longer period of time, 18ct gold has got what it takes to hold its own.
If you're thinking of an intricate design like one of our engraved bands, there's no question about it: 18ct gold is the only option for you. On the other hand, if you're envisaging something rustic and textured like one of our hammered bands, whose surfaces cleverly absorb day-to-day knocks and scrapes, you could just get away with a lower-carat alloy.
The more gold in the mix, the higher the carat weight and the higher the cost. Generally speaking, 18ct gold costs around twice as much as its 9ct gold.