Original poster: "resonance" <resonance@xxxxxxxxxxxx>It works best to have a reasonably large mass to maintain the rotational inertia --- helps with the balance -- sort of a gyro effect even at low speeds. That's why solid copper seems to work good or copper plated steel.
Dr. Resonance
But here's the question.. does your egg have to be conductive or magnetic? Why not aluminum, which is still cheap, also easy to machine or cast.