How to tell if gold plated parts are brass vs. steel

Is it true that a gold plated brass component with nickel undercoat can be attracted by a magnet? If so, how can I distinguish between a gold plated steel component and a gold plated brass component with a nickel undercoat using visual methods (e.g. by using a magnet)?

First of two simultaneous responses -- +++

Weigh them. Brass is heavier than steel.

Jim Treglio American Faucet & Coatings Corporation Vista, California

Second of two simultaneous responses -- +++

The underplate of nickel on brass is so very thin and the nickel itself is so weakly magnetic that the force will be almost impossible to observe or measure by conventional means. So, if there is an evident attraction, it most surely comes from a magnetic solid metal under the gold such as iron or steel.