Karat Gold Options

An 18k wedding set.
A common question for customers considering a jewelry purchase is which karat gold to choose. 10k, 14k, and 18k are the most common options in the United States, but what do those numbers mean, and what is the best choice?

 

Karated gold, which is almost always used for jewelry purposes, is an alloy of pure 24 karat gold and other metals which add desirable strength and durability to the jewelry. Studies have shown that with all things being equal, the gold content of an alloy does not seem to affect its durability. What you are really talking about are the alloys used in the karated gold.

The three most common and abundant alloys we find in karated metals are silver, copper, and nickel. Among the three, nickel is the toughest, and also the hardest, followed by copper and then silver.

Nickel is found only in white gold. It has a profound bleaching effect and when added to yellow gold even in small amounts has a significant effect on the color of the metal.

Nickel aside, we are left with copper and silver. With these two allows, it is possible to make an 18k alloy as hard as a 10k allow. When you combine copper and silver in equal amounts and then add the alloy to gold you end up with a karated metal that has a very hard quality. As you increase the silver content the metal tends to become softer (in 18k) and greener in color. In the United States, the 18k gold that has a slightly green tint is favored over the deep yellow color that is favored in Japan.

In 18k gold there are two popular blends: the first favored for color in the US and the second by Japan. The gold content is 75% for both. The silver content in the first sample is 16.6% and the copper content is 8.4%. The second sample has equal silver and copper contents of 12.5%.

In sample of 14k we have a pale yellow, with 25% silver and 16.6% copper, and then we have the alloy percentages reversed and a dark yellow color. In the 10k alloys, we find the one with the greatest popularity has a 11.5% silver, 40.3% copper, and 6.5% zinc content. Zinc is added to reduce oxidation during the melt.

If we compare the wear hardness of the various karatages, we will find that the second 18k alloy, the first 14k alloy, and the 10k alloy will have similar wear characteristics. Where they will differ significantly is the resistance to stress corrosion.

The 10k alloy is very susceptible to stress corrosion. It tends to react with body acids in some people, and they may have a reaction to the jewelry. It is for this reason that earring posts are commonly made in 14k. when the gold percentage reaches and exceeds 50% the reactivity of the metal is reduced and becomes stable. This is not the say that some people will not have a reaction to 14k (53.8% gold), it just means that the metal will not readily react with oxygen and body acids. Rarely do we hear of someone that has an adverse reaction to 18k.

When you look at making a decision based on wear characteristics alone, there is not enough difference to favor one karat over another. If you view the issue from the standpoint of which will give you the lowest reactivity rate, the 18k wins hands down.

Gold is alloyed for a variety of reasons, and you must decide as a consumer which reasons mean the most to your jewelry purchase.