# Which karat gold is harder, 24 kt or 18 kt?

$\pu{24 kt}$ gold indicates that $24/24$ part of it, i.e. $100\%$ of it is gold. $\pu{18 kt}$ indicates that $18/24$ part of it is gold. As gold is a soft element, I reckoned that $\pu{18 kt}$ gold would be harder than $\pu{24 kt}$ gold.

I recently saw on a website that $\pu{18 kt}$ gold is harder than $\pu{9 kt}$ gold, which surprised and confused me. Now I want to know which karat gold is harder of $\pu{18 kt}$ and $\pu{24 kt}$.

• If you reckon that 18kt gold is harder than 24kt gold, why are you surprised that 9kt gold is harder than 18kt gold? – Jon Custer Jun 26 '18 at 15:02
• Addition of any alloy , usually Cu, Ni, Ag, Zn, and others, will harden pure gold by solid solution. And pure gold or any alloy can be hardened by cold work. – blacksmith37 Jun 26 '18 at 16:12
• Since the carat scale only tells you about the amount of gold but nothing about what else is in the alloy, it won't directly relate to the hardness (there might even be some alloys softer than gold, though they would be practically useless so probably rare). – matt_black Jul 12 '18 at 14:56
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