Yellow gold-filled chains are made with 14/20 yellow gold-filled wire. Gold-filled, or gold overlay, is made by heat- and pressure-bonding a thin layer of karat gold to a brass (or other base metal) core. The "14/20" notation refers to the industry shorthand describing the resulting material. The first number is the karat purity of the gold used; the second number is the amount, by weight, of gold to the substrate material. "14/20" gold-filled material is made with 14-karat gold and the gold represents 1/20th (or 5%) of the total weight of the material. 14 karat gold covers the brass surface, making it tarnish-resistant. The value of gold-filled is greater than gold-plated because gold-filled has an actual layer of karat gold, not just a microscopic film that will easily wear off. Gold-filled is more economical allowing you to enjoy the warm tones of gold at a fraction of the cost of pure gold.