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Horology 101 - gold

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Published on 08-04-2008 05:05 PM

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All gold is not created equal. Well, not after its purity is diluted. There are different alloys classified as 18K and 14K, with different properties and colors depending on the metals used in the mixture. Copper, silver, and gold all have the same basic crystal structure which makes them ideal for combining. 100% pure gold is designated 24K, so 18K is 75% pure (18 divided by 24 is .750) and 14K is 58.5% pure. The following are typical ratios followed by the resulting color achieved.


75% gold + 25% silver = green

75% gold + 12.5% silver + 12.5% copper = yellow

75% gold + 9% silver + 16% copper = pink/rose

75% gold + 4.5% silver + 20.5% copper = red


58.5% gold + 41.5% silver = green

58.5% gold + 30% silver + 11.5% copper = yellow

58.5% gold + 19.5% silver + 22% copper = pink/rose

58.5% gold + 9% silver + 32.5% copper = red

(white gold has many more variables and will be discussed in another post)

Even though the same color designation is used, different purities can yield slight changes in the shades. For example, here are two yellow gold watches from the late 50's in nearly identical condition: on the left is an 18K case and on the right is a 14K case. Manufacturers choose their alloy combinations and not all used the same formulas.

Some other metals can be substituted for 1 - 2% of the silver to change the finished product's characteristics. Zinc is the most common additive and will increase gold's fluidity while in a molten state. This facilitates easier cast molding. The addition of nickel will increase strength. Iridium and/or cobalt will refine the grain. Rolex's patented Everose uses platinum to enhance the appearance and resist tarnishing.

I hope you enjoy our new weekly feature! If you have any suggestions or questions please PM me and we'll try to answer them in subsequent features.

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Horology 101 - gold
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