Gold Filled is an American metal manufacturing process and legal standard of quality . It differs greatly from gold plated. Gold filled is two sheets of solid karat gold (most popular being 14kt gold) bonded over (or for wire, rolled in tube) a core of brass.
For a piece of jewelry to be legally stamped with the telltale ‘GF’ marking, its weight must be at least 1/20th gold. This explains the typical stamp you would expect to see on gold filled articles: “1/20 14K GF”, which means that 5 percent of the piece is 14 karat gold. Due to the surface layer of gold-filled jewelry being about 100 times thicker than any plating, gold-filled pieces tend to last much longer, and are considered ‘lifetime jewelry’.
Gold plated jewellery is made using a thin layer of gold to surround base metals or sterling silver. The fine layer of gold is set using the method of chemical or electrochemical plating. It is the cheapest of the three forms of gold jewellery (solid karat gold, gold filled and gold plated), and is the quickest to tarnish.
When sterling silver is used as the interior metal, with at least 2 microns of gold plating, the item is primarily labeled as Gold Vermeil. Gold filled is not to be mistaken for gold plated over sterling silver – which is far less expensive than gold filled. A number of resellers in the industry have confused the market place by using those terms interchangeably. American standard gold filled does not have any sterling silver in it, and although it is more expensive, it lasts far longer than gold plated over base metal and over sterling because it has 100 times more gold than any possible plated process. How long gold filled or plating lasts depends largely on the chemical makeup of and the care with which the person wearing the jewellery takes – which varies widely.