Sometimes called silver-gilt, the techniques that eventually evolved into vermeil date to at-least the 4th century BCE. Ancient Romans overlaid hammered gold leaf, Incan's used depletion gilding, Chinese "ormolu" used gilt-bronze and Korean's "keum-boo" was a method for silver-gilding.
Vermeil (pronounced ver-may) is high karat gold on top of a 925 sterling silver base. Its a gold plating/filling technique, but where gold plated jewelry can use various base metals and has no minimum depth, vermeil jewelry always uses hypo-allergenic sterling silver as a base metal, and is at least 2.5 microns thick.
In 18th century France, artisans evolved these metal working techniques to eliminate the use of mercury and gold vermeil was born.
The Museum of Jewelry uses 24k gold on a 925 sterling silver base for all of the handcrafted gold vermeil jewelry shown.