Gold Plated vs Gold Filled
Gold plated objects have a gold layer chemically bonded to a base layer, gold filled objects have a gold layer bonded mechanically to a base layer.
Anything that is labeled gold-filled is made with a hard metal base layer covered with an outer layer of gold. The gold must be mechanically bonded to the metal base through the process of soldering, rolling, or drawing.
Gold filled objects are usually heavier than gold plated.
Gold plating is a process in which a piece of jewelry, usually made of bright nickel, is placed in a gold bath. The depth of the gold overlay dictates how the jewelry is marked.
Gold-Flash: 2-4 microinches of gold over bright nickel.
Gold Electroplated: 7-30 microinches of gold over bright nickel or sometimes silver.
Heavy Gold Electroplate: 100+ microinches of gold over bright nickel or sometimes silver.
When gold is plated over stainless steel, the jewelry will be marked as hypo-allergenic.