In the mid-18th century the process of fire-gilding was developed in France. Later on it was discovered that workers involved in this work became blind due to their exposure to mercury which was used in the process & it was banned. In modern times electrolysis is used to bond the gold. This method is safe. Vermeil jewellery has been popular since the 19th century & it has gained great popularity as it makes gold collectibles more affordable.
Often there is confusion about vermeil (ver-mey) & gold plated items. When a piece is said to be vermeil it can only have a sterling silver base. Gold plated items may have a base coat of metal, for example you can apply a layer of gold to base metals like, pewter, copper & brass. Often gold plated items have a very thin coat. In order for an item to be correctly described vermeil it must have been used to plate high grade .925 silver. The gold layer must be 14ct of higher in purity. The layer of gold must be at least 2.5 microns thick.
Gold plated items can be less than 0.5 microns thick. Vermeil & gold plating involves fusing gold onto another metal - in the case of vermeil this is sterling silver. Vermeil pieces have a much higher value than gold plated items because of the sterling silver contained in the piece & also because vermeil is much more durable. Gold plating will often fade / wear & the piece will need to be re-plated.