The soft, black sublayer under the gold on a piano plate mentioned by Andy
Taylor is filler used to smooth out the natural sand finish of a casting;
also used on sewing machines and other cast iron consumer goods in the old
days. One brand is 'Keystone Filler'; my granddad told me about this. When
he started as an apprentice in 1892, industrial machinery was so treated,
then Japanned, polished, and trimmed with gold pinstriping. I think antique
touches of craftsmanly aesthetics like this are part of the charm we find in
old MM objects.

I am off to Mother India this afternoon. I will be on the lookout for MM or
MM people there, and write a report when I get back. I am afraid that it
will not take up much space. Maybe I will spot an interesting Raj-era
electric fan for Durward Center though; India has a surprisingly long
history of really weird domestic electrical apparatus. Personal e-mail for
me will be forwarded thru the office net by my son, and I will read MMD
from the Index whenever I get a chance.