W.C., your advice is gold worth to me! Thank you! I can find it locally, and may be able to coax them to sell to me (they only sell to industries), too, if I know the micron size! So, if I want finger-bleeding size, somewhere between 30 and 45 micron would be good.
I picked up that the brown aluminium oxide is more abrasive than the white, which corresponds to the two samples of Wallis that I have, where the Belgian mist is really aggressive while the white is similar to Fisher 400, and Fisher 400 is similar to Uart 400.
New possibilities!
Charlie