I suspect the lead works because any vibrations just plain die because the energy does into non-elastic deformation rather than getting transmitted because the deformations are elastic.
It's not the mass but rather the malleability that does it.
Reductionist and proud of it.
Being ignorant is not so much a shame, as being unwilling to learn. Benjamin Franklin
Chase after the truth like all hell and you'll free yourself, even though you never touch its coat tails. Clarence Darrow
A person who won't read has no advantage over one who can't read. Mark Twain