very funny Limy, have we begun drinking over there? (assuming we had stopped!!)
the overview, for those new to vibratory finishing, there are 4 basic types of media used in them for metal finishing, in order of aggressiveness,
1) hard ceramic media, basically like throwing rocks in with the parts, but do come in various grits,
2)cast abrasive "nuggets", pyramids or cubes of plastic with (varying) abrasives mixed in. the plastic can also vary in hardness.
3) burnishing shot, usually steel or preferably stainless steel, that come in various shapes and sizes, from balls to flying saucer like shapes, to tiny needles, to accommodate parts with corresponding degrees of nook and cranny-ness. these always have a mirror polish (when new). this produces the classic "tumbled' finish on mass produced jewelry.
4) dry media, usually corncob or walnut shell, and often used with rouge, as a very light cleanup and polish. this is the media for processing used brass cartridge cases that many are familiar with here, and is not really an industrial metal finishing process.
(for lapidary applications, stone finishing is accomplished wet with a load of stone, usually of the same type, either rough, or preformed to some extent, and bulk abrasives, such as 80 grit silicon carbide, and step finishing down to a polishing media, but that is a different animal.)
the first three metal media are used with a "bath" that is usually water with additives (surfactants and or soaps). for maximum effectiveness the heavier industrial units have a "flow-through" setup that allows the metal removed to be "settled out" and the fluid returned. that prevents it from becoming a useless paste that gums up the action.
the degree to which the details are "blurred" or rounded over of corse varies with the aggressiveness of the cut and the time processed, and must be balanced with the work needed to accomplish the necessary finishing and deburring. having parts with a decent surface finish and only light burrs, using the least aggressive media, and not working it longer than needed will produce the crispest edges.
for finishing most of the machined parts we commonly would encounter in the 1/4 to 1- 1/2" range, with a decent quality finish from the last cutting step, I would think a medium grit plastic media would be a starting point.
for soft-ish metals (brass, nickel silver), small parts for musical instruments, I might try a burnishing media first, (I.E.,shot tumbling)
wow! didn't mean to get that long winded.. but hope its helpful..