Cork belts IIRC came from SR Johnson. They are used in the glass industry.
When you look at a cork belt they look like they are all 36 grit and look super course. Cork belts have to be broken in, on Trugrits website they have SR Johnson break in protocol.
I use them with and without compound from 200 grit to 1000 grit.
When you break in a belt SR Johnson uses a flat bar of steel, I use a round bar of steel. I find the round bar smashes down the pikes instead of shaving them off.
Standard break in is put your grinder on High speed and use green compound on the belt, then use the bar of steel and lean into the belt for a solid 10 minutes on a contact wheel by the clock and let that bar smash belt for the entire time.
I use a round bar and do the same with and without compound depending on the finish you want. No compound and the belt leaves a fine satin finish with compound it will polish the blade.
It is easy to go to mirror finish by using a 400 grit belt and 1000 grit belt with green compound then take it to the buffer for a couple of minutes, or take it to the bench and hand sand to satin in a few minutes