I can't seem to solve this despite asking many people.
The 10 year old coating makes the bronze
prop look like its made of aluminium.... actually, I thought it was aluminium until I tried to make it smoother with a polisher and cutting paste... I then discovered that it was only a coating.
is aluminium, so maybe this was done on purpose.
The coating is conductive and does not easily come off.... the wire brush on the angle grinder has no chance for example. It is a seriously hard, well stuck on coating.
So now I have the prop with a bit of polished bronze
showing through which is a problem as the antifoul does not stick here well.
I am now so impressed that I would like to put this coating back.
Any ideas anyone ?