Gold leaf you've probably heard of, but it's possible to get very thin sheets of several different pure metals: Click the Sample Group link below to see all the ones I have, which represent pretty much the complete list of those that are commercially available. (Many, many different mixed alloys are also available in leaf form.).
Palladium leaf may seem exotic at first, but it's actually quite commonly used as an alternative to silver, because it looks similar but does not tarnish. For outdoor applications, for example, you cannot use silver leaf. This may be one of the few instances where a truly precious metal (comparable in price to gold) is used to imitate a far less valuable one (silver is usually about 1/70th the price of gold or palladium).
Leaf like this is so thin it has to be picked up with special Red Squirrel hair brushes (none of that Gray Squirrel crap, mind you) and when it wafts down onto an object it conforms to the shape of the surface, settling in even to details as fine as a fingerprint.
I bought this leaf from a store in New York when I was visiting there with my six-year-old daughter Addie: You can read about our visit here.
Source: New York Central Art Supply
Contributor: Theodore Gray
Acquired: 11 July, 2003
Price: $48/25 sheets
Sample Group: Metal leaf