Gold fill is a manufacturing process invented in Japan whereby a gold "sandwich" is created, gold on the outside and a base metal on the inside. The gold is permanently bonded under enormous pressure to the surface of the base metal in a milling process which results in a gold surface about 100 times thicker than conventional gold plating. The material produced is about 5% gold, so is much less expensive than solid gold. But it is far more durable than mere gold electroplating. In appearance jewelry produced with 14kt gold fill is identical to jewelry produced with 14kt solid gold. The only way to tell them apart - even for a jeweler - is by the stamping indicating it is gold fill not solid gold. And even in the most extreme circumstances, gold fill will not "wear off" as is commonly the case with items which have been merely gold plated.