Cast iron is actually quite a good platter material, in that it is less resonant than most materials. The trick is to keep it away from the cartridge, with, say, a 1 inch graphite upper platter. Nottingham Analogue does this, and it works very well indeed.
Turntable Platter Demagnetizing
I was wondering if I use a tape deck head Degausser if that would demagnetize the turntable platter. Anyone out there have some thoughts on this also any other ideas about this matter ?