Angie, metal covers for icons are either individually made by skilled tradesmen for a specific icon (such as for well-known historic, painted icons), or are mass-produced in workshops to a template for a particular icon print. The latter are usually made of an inexpensive soft base metal which is then plated with silver, or a non-precious metal which resembles silver.
Metal the thickness of foil is too flimsy to keep its embossed shape, unless it is supported from underneath.
At any rate, the beauty of an icon comes not from any cover, but from what is painted or printed on it. Moreover, covering an icon with a metal cover, even a printed icon, robs the icon of the ability to truly express what it teaches.