THis is an experiment involving a electric shaver coil meant for 115v run at 50vac.  The output into 100ohms without a shield is about 16v
3x5 paper card down to 12v
thin copper 13v
1/8" brass 7.5v
heavy copper 13.5?  its strap so there mgiht be flux lines around it
altoids tin 6 volts with significant distortion at the peaks (its also squawking a lot)
1/8" aluminum 7v, smooth sinewave and a little bit of vibration at 60hz
big sheet of 16ga? brass 9v
1/8" mild steel 3v 
one sheet folded 13 trying first datapoint again
11.5v
4 sheets folded 11.5
16 sheets folded 10.2v (with some even? distortion/flattening at the tops
16 sheest some cut apart 9.4v same kind of distortion
tin plated lid has the same distortion as the altoids tin
CD 8.7v a tiny amount of flattening distortion

Here is the tin response, the more I think about this, the more I think its just the thinness of the steel, and nothing to do with the tin.

    Oh this is cool. I can raise the first hump and lower the second hump by putting a strong electromagnet on the secondaries core. (reversing the magnet raises the second hump and lowers the first. (opposite on - wave)
  for the tin the distortion looks more asymmetrical at lower voltages and more symmetrical at higher voltages (but other than that nothing that grabs me visually
10ohms makes the distortion more asymmetrical and less proportionately however in a different way than the magnetic field (ie. the first bump in both the + and - wave is the smaller one)
open circuit makes the distortion component reach almost down to 0 (ie. the distortion is at a maximum)     i.e. its a good frequency tripler
Here is the unloaded secondary coil with tin 'shielding'

Here is the unloaded secondary coil with a 4.7uF cap in parallel with tin 'shielding'