Aggressive mineral grit strips heavy rust and mill scale off structural steel fast, and it is what most people picture when they hear "sandblasting." Glass bead does the opposite job: a smooth, satin finish that cleans without removing base metal, used where you want the part clean but not aggressively profiled.
Soda blasting is soft enough to strip paint from aluminum, fiberglass or even wood without warping the panel or eating the surface underneath - the detail that separates a trade from a rental hose. Walnut shell and corn cob step down further still, for delicate cleaning where almost nothing can be removed but the coating. The wrong media on thin sheet metal will warp it permanently, which is exactly why this is not a weekend project.
Blasting also leaves a measured surface roughness, or profile. Too smooth and a new coating has nothing to grip; too aggressive and the part is thinned. Matching profile to the coating that is going on next is the technical heart of the trade, and it is why we coordinate timing with whoever coats your part - bare steel starts rusting within hours of blasting.
