• Color
• Purity

Gold purity is measured in karats. 24-karat gold is pure gold, but its purity makes it more expensive and less durable than gold alloyed with other metals. Different alloys are used in jewelry for greater strength, durability, and color range. Pure gold is too soft to withstand everyday wear and tear, so it is alloyed with silver, copper, nickel, and zinc to increase strength and durability. Karat age, noted by a number followed by "k," indicates purity, or how much of the metal in a piece of jewelry is gold. Karat age is expressed in 24th, making 24k gold, 100% gold.