Gold Alone Is Too Soft to Wear, Which Is Why Jewellery Isn't Pure

Pure (24-karat) gold is mechanically soft enough that a ring made from it would scratch and deform in ordinary use, which is the real, practical reason jewellery alloys exist, not purely a matter of cost.

Karat as a precise fraction, not a marketing term

\text{Karat} = 24 \times \frac{\text{mass of gold}}{\text{total mass}}

The karat system expresses gold content as a fraction of 24. 18-karat gold is 18/24, or 75%, gold by mass, with the remainder usually copper, silver, or both, chosen specifically to harden the alloy through solid-solution strengthening.

24k

Pure gold

softest, most malleable

18k = 75%

Common jewellery grade

14k ≈ 58.3%

A harder, more durable grade

Why alloying actually hardens it

Adding copper or silver atoms into gold’s FCC lattice, the same structure covered on this material’s materials science page, distorts the regular atomic spacing locally, and those distortions resist the dislocation motion that lets a metal deform easily, a real strengthening mechanism, not a dilution. This is why 18-karat gold jewellery holds its shape and resists scratching far better than the same item made in 24-karat gold would, at a real, measurable, and predictable cost in softness and malleability as the gold fraction drops further toward 14-karat or below.

Sources: karat definitions and alloy hardening mechanisms draw on standard jewellery metallurgy and materials science references.