A Sand Blasted finish is open and porous.............The higher the Air pressure, the rougher the finish with any Sand ,, and the larger the sand grain the rougher the finish.
Glass Bead Blasting is done with Glass beads that don't generally cut and open the surface like sand, and the air pressure and bead size can be adjusted to vary the finish. Glass bead is more of an impinged or peened finish. and will not show finger prints and trap dirt like a sand finish will.
If you want a fine closed pore finish, I'd ask the operator to use a fine (small) glass Bead at a low to medium air pressure................The required air pressure will vary with blast nozzles and equipment as will the air pressure.
I hope this helps you,