Gold Fill

Gold-filled metal may be more practical for everyday items that tend to receive more wear, like rings and bracelets. Gold-filled requires some special care to keep the gold layer intact and unmarred for your designs. Gold-filled sheet and discs are available in single-clad and double-clad varieties.

Gold filled products are created utilizing a process that starts with a base metal such as brass (i. 90% copper and 10% zinc) or nickel on which a thin sheet of karat gold of the desired thickness has been "welded". Gold filled jewelry is NOT gold jewelry. Gold filled jewelry is sometimes referred to as “rolled gold” and refers to a very thin, solid layer of gold that is bonded to a base metal such as brass or even silver. This is a durable piece that will not tarnish or chip. It is also safe for those with metal allergies. Gold-filled stock should be stored in a dry place. The outside layer is karat gold, so it will not tarnish as quickly as sterling silver. However, tarnishing elements act very slowly in the absence of moisture. 

Gold-filled wire, sometimes called rolled gold, is a wonderful choice for wire jewelry makers. It is appropriate for all types of jewelry. For most people, it will last their entire lifetime without showing signs of wear. It is made by forming a tube of gold and filling the tube with a base metal, usually jeweler's brass. Gold-filled is constructed in two or three layers. The core metal is jewelers’ brass. Single clad gold-filled has all the gold content in a single layer on one side. Double clad gold-filled splits the gold content into surface layers on both sides of the material. The gold alloy is then bonded to one or both surfaces of the brass core with heat and pressure. The bonded raw material is then sold as sheet or wire to jewelry manufacturers for use in designs. Gold-filled items have a much thicker layer of gold on them, and the gold is a much higher quality. In fact, it is just a step down from solid gold when it comes to quality and value. Speaking of solid gold, pure gold is very soft and is not a good choice for jewelry; that is why an alloy is almost always used for gold jewelry items, even in jewelry pieces worth an incredible amount of money. Gold-filled cannot be cast. This is a major limitation in the types of products that can be manufactured in gold-filled. Products must be made from sheet, tube or wire that retain the layers constructed in brass and gold. Casting by definition is melting the metal material which would alloy the layers into one big melted mess. 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" or "12/10" 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. You may occasionally see other notations, too; each will inform you about the material's make-up. For example, "14/40" gold-filled is composed of 14-karat gold that represents 1/40th (or 2.5%) of the overall weight of the material.
What's the Difference between Gold Plated and Gold Filled? http://www.bmjnyc.com/blogs/blog/15888648-whats-the-difference-between-gold-plated-and-gold-filled
Gold-filled metal may be more practical for everyday items that tend to receive more wear, like rings and bracelets. While gold-filled jewelry is a relatively affordable option compared to solid gold, solid gold jewelry is ideal for investment pieces and any item that may hold sentimental value, like a wedding band or engagement ring.

Gold-filled items contain significantly more gold than gold-plated metals. For this reason, gold-filled jewelry is more durable, valuable, and expensive than its gold-plated counterpart. Gold-filled metal is at least 5% gold; this higher quantity of gold helps protect the piece from tarnish. The thicker layer of gold is usually an alloy (i.e. gold blended with another, stronger metal).
Since gold-filled material has an actual layer of solid gold on its exterior, the material can hold up for years even if worn daily. To keep your gold-filled jewelry looking new, simply wipe with jewelry polishing cloth. Ammonia is also helpful in keeping a brilliant shine. First, Gold-Filled jewelry is not the same as Gold Vermeil.  We've seen jewelry designers interchange the terms "Gold-Filled" and "Gold Vermeil" and want to stress that these are two very different processes in the world of jewelry manufacturing. They also result in two different products of different price points and durability. "14/20" gold-filled material is made with 14-karat gold, and the quantity of gold represents 1/20th (or 5 percent) of the total weight of the material. You may occasionally see other notations, too; each will inform you about the material's make-up. For example, "14/40" gold-filled is composed of 14-karat gold that represents 1/40th (or 2.5%) of the overall weight of the material. Regardless of brand, gold-filled jewelry is coated with a layer of gold, which must be at least 10k gold and 5% of the total weight of the piece. Gold-dipped, on the other hand, could either be gold-washed or gold-plated. Both have a thin layer of gold, applied to the base metal by dipping (the liquid is chemically charged so that the gold sticks). The layer of gold is even thinner for gold-washed than it is for gold-plated; and either easily rubs off with frequent use. If handled properly, gold-filled should require only buffing. Polish lightly or tumble finish instead of using more direct buffing. Tumbling in steel shot is a great option because it’s a non-abrasive technique, so there’s no chance of removing the gold layer. Keep in mind that tumbling in steel shot will not remove scratches, so it’s important to avoid scratching the material as you work with it. Typically, double-clad gold-filled sheet stocks are used on items to prevent any discoloring or to enhance its value (e.g. cigarette case). Since the edges of the gold filled sheet stock are sometimes exposed, supplementary gold plating is often necessary to "seal" the base metal core to prevent any chance of corrosion or discoloration. Use extra care when soldering gold-filled materials. Any blemishes you create will need to be sanded out with great care to avoid exposing the brass core. Use a firescale retardant such as Stop-Ox II™ to avoid having to do heavy finishing to remove firescale.