I need to lap the ID of an aluminum piece out about half a thousandth.
It is heavily annodized, and has a matte, frosted finish. I think the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm wondering
what sort of abrasive I should try. Given that annodizing itself is very
hard, I don't know if normal compounds will touch it. I'm also not sure
how fine I should start with. This is a one-off, so I don't want to have
to go out & buy several grades of diamond paste. I have a "sample" kit
of Clover lapping compounds, which includes silicon carbide, and possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White