for delicate metals, or where you don't want much surface distortion use a soft plastic bead, like polyethylene (pet), you can also use natural media like walnut, almond or pecan shells, run lower pressure, and use a tip with a larger aperture .

I would avoid glass media IF the piece is going to be painted or powdercoated, as I believe it makes the surface smooth and "slippery" (at least this is what my powdercoater tells me) but could be ok if the piece is going to be polished. (a test panel will tell all here)

as in the above post, baking soda (this ain't arm and hammer like in your fridge, it's more like super coarse salt) can also be used with almost NO surface distortion, BUT, if the piece is going to be painted or powdercoated there is a neutralizing wash step that must be performed or adhesion suffers (readEELING IN SHEETS)

now, it's extremely wasteful $$$$$$ to just blast and not be able to re-collect the media, so blast on a tarp up against a wall so you can recover the media, because you will find that you'll empty that small sand blaster in about 1 minute and the frame will about 1/10th done, so either recover the media so you can collect and refill, or buy 9 bags of blasting media.

I like the above idea about using media blasting as a diagnostic procedure, to determine the integrity of the frame,..and I doubt using any of the above media that you could remove a measurable amount of metal, even if you just sat there for 10 minutes in one spot, with any home sized media blaster.

industrial units are another story and can be set up to cut through anything, like your boot with your foot and all in less than a second, if you don't pay attention and miss.

most places that offer media blasting really know their stuff, pay em a visit with a small part, get a quote and ask some questions.