I'd never have thought of "dating by darkening" as Graham suggests-thanks for posting the link
]. If it's a 1954 set, there's only five years to blacken the speaker outline but that was different times-coal fires etc
Would it be the spkr magnet attracting fine dust/metallised particles or is it warm air from the interior collecting on the frame as it leaves via the grill? I'm guessing a Console KB would be a relatively high end purchase then!
Dave
I think it's a great photo by the way!