Vermeil means gold plate over sterling, so "gold" is an unnecessary
modifier. There is no other kind of vermeil than gold over sterling.
Silver can tarnish through a layer of plating if the plating is not
thick enough. Gold electroplate is gas porous in thin layers.
You need to check your own country's marking laws to see what
thickness of gold is needed over the sterling to be legally marked as
In the US, for instance, to be marked as vermeil the gold plating
must be at least 2.5 microns thick. Also, if there is a layer of
nickel below the gold than that also must be disclosed. If you just
mark or advertise the item as vermeil, the gold layer must be
directly over the sterling.
Here is the relevant section of US law.