What is the difference between gold, gold-filled and gold plated?

Any item in my shop will be clearly listed as one of the following solid gold, gold-filled or gold plated.

With solid gold the higher the carat, the larger the percentage of gold. So 9ct is 37.5% gold, 18ct is 75% gold and 22ct is 91% gold.

If an item is listed as gold-filled all components are created using gold-filled materials. Gold-filled or rolled gold material is created using a base metal, such as brass. Gold is then mechanically bonded onto the brass core using heat and pressure. In order for the material to be sold as gold-filled it must contain at least 5% or a minimum of 1/20th gold.

Gold plating is a process that uses an electrical current to produce a thin layer of gold over an item. Typically the item is either copper or silver and the layer of gold is 2 or 3 microns thick.