In the United States the purity of gold is designated by karat. Pure gold is 24k, but, because of its softness, it is not suitable for making jewelry. Other metals such as copper, silver, nickel, and zinc are added to gold to strengthen it. What is added and how much is added determine the color and karat of the gold.

To make this easier to understand let's take an imaginary ring and examine it. The color of the metal is immediately apparent. Gold comes in several colors, but let's pretend that this ring is pink gold. Inside the ring is stamped 10k. What do these things tell us? First, that the gold was mixed with copper, silver and zinc to make yellow gold. The pink look was achieved by using a larger quantity of copper. The 10k mark assures that 41.67% of the metal is pure gold, and the other 58.33% is copper, silver and zinc. It also indicates that the piece was made in the United States. (other countries do not use 10k). A 14k stamping would mean that the ring contained 58.33% gold and 41.67% other metals. If the ring was marked 18k, it would contain 75% pure gold and 25% other metals.

In Europe gold is stamped according to its fineness. Pure gold is 1000 fine; 18k gold is 75% or 750 fine. Consequently, an 18k ring made in Europe would be stamped 750. Below is a chart of the most common karat markings