Category #6
A Jeweler's Tidbit
of Knowledge

     If 18K (75% pure gold) is softer than 14K (58.3% pure gold), will it wear out faster? Is 14K stronger? The answer to both questions is NO.
     The word "soft" when applied to precious metals is not referring to its longevity or durability. Rather, it is describing, in lay terms, the metal's malleability and ductility properties ( the metal's ability to be bent, stretched or flattened without cracks or breaks). Pure gold (24K) is the most malleable and ductile of all metals. In fact, pure gold can be flattened to such thinness (only a few molecules thick) that it becomes nearly transparent!
     Density is the key word when thinking of longevity and durability. Density is the mass of an object per its volume. And because all alloys (other metals such as copper, silver, zinc, etc.) added to 24K gold to reduce its purity are less dense than gold, the resulting lower karat is also less dense. Thus, an 18K piece of jewelry has more molecular weight (and density) than the same in 14K; more molecules to wear off.
     So why not use pure (24K) gold for jewelry? Because pure gold is so "soft" that it has a hard time keeping its shape and surface condition (polish) when worn. Alloys are valued additives that not only reduce the price of jewelry, but "harden" the gold to provide rigidity and better polish. Alloys also offer an ability to change the color of the pure gold to pink, green, white, and yellow karat golds. But it doesn't take much (of additional alloys) to improve pure gold and make it more usable. Most of the gold coins the US Mint struck, historically, were .900 fine gold (21.6K).
     I, (and as it happens, most of the world) tend to use 18K for the majority of jewelry I make. It's a good blend of economy over higher karats which could be used, but still high enough to have the noticeably hefty feel and rich look of GOLD.