10-karat gold is an alloy made up of 10 parts gold and 14 parts other metals such as copper, zinc, silver or nickel. In percentage terms, 10K gold contains 41.7% pure gold.Jewelry that is 10K gold will usually be stamped with a mark such as 10KT, 10K, 10kt or something similar. If you see a mark reading .417, this also means that the item is 10 karats gold.n percentage terms, 10K gold contains 41.7% pure gold. Jewelry that is 10K gold will usually be stamped with a mark such as 10KT, 10K, 10kt or something similar. If you see a mark reading .417, this also means that the item is 10 karats gold.