When gold is plated onto the surface of another metal, it is a microscopic film of gold, and easily scratches or wears off over time. This means that a layer of gold has been bonded onto another material, usually brass, by treating the metals with heat and pressure bonding a thin layer of gold onto the top of the core metal. Jewelry made of gold filled wire or sheet can withstand more wear than gold plated, but still can scratch, and cannot be hammered, or the underlying metal will show through. But, since gold filled wire contains little actual gold, the price of the material is so much less expensive. This term defines how much gold is actually in a piece of metal.
Gold is mixed with various other metals, in various percentages.
Yellow gold is gold, copper, silver, and zinc. White gold is gold, copper, nickel, and zinc. 10K gold contains 41 percent gold, 12K 50 percent gold, 14K 58 percent gold, 16K 66 percent gold, 18K 75 percent gold, 20K 83 percent gold, 22K 91 percent gold, and 24K gold is 100 percent gold. 24K gold is rarely used because it is so soft. The more gold present in the material, the more valuable, and the quantities and mixtures of base metals will show as different colors.