Andy Taylor wrote:

> Hello,  I have noticed that piano plates are coated with a thick
> black pigment, sort of like a thick primer, to be able to obtain
> a smooth finish on the rough casting.

Piano plates might use something special, but on machine tools (which
also have their aesthetic qualities) they use Bondo acrylic auto-body
filler or the equivalent.  Its natural color is sort of a sickly pink,
so it has to be painted.

Mark Kinsler