Karats refer to the fractional parts of pure gold in the total alloy. The remaining parts are alloy metals to make it harder and more durable. Pure gold will not tarnish. However, lower karat alloys can tarnish in certain conditions, but tarnish will be slight to non- existent in 12K and higher alloys. The wearing of gold jewelry usually keeps it clean and bright.
Gold is alloyed to meet certain market and engineering requirements.
All yellow gold contains copper and silver in its alloy. By varying the amounts of copper and silver, you can get pink or green gold. The more copper in. Many people ask where the gold comes from. It is delivered to an alloy house which adds the alloy to make it into gold karat, the amount of alloy depends on the karat desired.