Here what they say about soda, keep in mind there are different grits:
"What is soda blast? Soda blast is a sodium bicarbonate product. It is a non hazardous, environmentally friendly blasting media that is used to strip graffiti off of walls, clean fragile aluminum parts such as auto parts, or any other delicate surface where damage to underlying structure is a concern. You can even strip paint off an aluminum paint can at 10 psi without damage to the can!
If you must have a diamond media, here it is:
" Resin and Metal bond diamonds are very popular abrasive media for free abrasive lapping and polishing applications, suitable for very tight tolerances and very high surface finish applications. They are also a popular free abrasive media to be used with oil, glycol and water based vehicles for lapping and polishing of various materials such as ceramics, carbides and sapphires, etc.
They also sell media for dermabrasion - human faces - so I think that would not hurt scratchings in metal.
