18 Karat Gold
75% gold. Harder and more durable than 22K, which is why stone-set and Western-style jewellery uses it.
18K is 18 parts gold in 24, hallmarked 750. The extra alloy makes it meaningfully harder and more scratch resistant.
That hardness is what lets it hold prongs, pave settings and fine detail without bending, so almost all diamond jewellery is 18K or lower.
The colour is a paler, cooler yellow than 22K, and it is the base for most white and rose golds.
When you are buying
For anything with stones, and for a piece that will be worn every day for years, 18K is the better buy even though it contains less gold. Durability is worth more than a resale line item you may never use.
750 Gold
The hallmark number for 18 karat gold, meaning 75% pure.
Karat
The purity of gold, measured in twenty-fourths. 24K is pure gold; 22K is 22 parts gold to 2 parts other metal.
22 Karat Gold
91.6% gold. The Indian standard for traditional jewellery, and what a 916 hallmark means.
14 Karat Gold
58.5% gold. Hard, durable and common in export and Western jewellery, less so in India.
White Gold
Gold alloyed with white metals and then usually rhodium plated. The white you see is a coating, not the metal.
Rose Gold
Gold alloyed with a high proportion of copper, giving a warm pink colour. Harder than yellow gold.