Gilding is used to cover large areas with a thin layer of gold. Gold hammered into very thin sheets called 'gold 'leaf' is attached with adhesives. Gilding is also done with gold dust mixed into a paste with other substances. Items are also covered with thicker sheets of gold by hammering and forming it around the item. This is called gold rolled. With the application of heat and pressure, gold sheets are fused to the object. This is known as gold filled. But the most used process, especially for intricate jewelry, is gold electroplating.
Commercial applications for the electroplating of gold and silver began in the early 19th century. Simply put, electroplating works by immersing a metal object into a solution that has microscopic particles of gold suspended within it. A small electric charge is run through the metal object, and the particles of gold are 'attracted' to the object and bond with it. This very thin layer of gold can vary in thickness, and is measured in millionths of an inch, or micro inches . Most common gold plated objects have a coating that is 7 to 20 micro inches, and can be 10 to 14k gold.
Vermeil (pronounced 'vermay') gold is a much thicker layer that is at least 100 micro inches thick. Vermeil gold jewelry is much more durable than regular gold plated jewelry, where the coating is so thin that it is easily worn off. Regular gold plated jewelry is usually done over lesser metals such as brass. Vermeil gold jewelry is always at least 14k gold and is done over sterling silver. It is very high quality, and has the beauty of gold without the high price of solid gold.