... good stuff!
Also, check this little 'weirdness' out...
I've never seen this published anywhere, but here you are, guys, just for you!
Take a 10p coin. Explain to the speccy that it's quite light, because it's made out of a light metal. As you ask them to feel it's weight, perform a false-transfer and stuff a 2p into their hand. Ask them to grip it tightly... this is important.
Now, gesture for them to turn their hand with the back of the hand towards the floor, still gripping the coin.
With an SSUD up your sleeve
bring it close below the back of their hand.
Explain that Alchemists could change the properties of metals, blah blah, and go on to say how some metals are HEAVIER than others.
Suggest the coin is getting heavier. Of course, it will be, as the forces of magnetism go to work on the copper plated 2p, which is actually ferrous (attracted to magnets) inside.
Say that 2p's, because of their value being less than a 10p, are made of a cheaper metal, which is heavier than the posh alloy 10p. When they open their hand, voila.