Any kind of aggressive blast media "peens" the metal and results in a lot of distortion- - - -problems that sometimes don't show up until the final finish is applied- - - -then sheet metal parts with big "flat" areas look like the craters on the moon. Professional blasting with baking soda or granulated dry ice is the safest, but also the most expensive approach. Using ground glass media in a recirculating blast cabinet (with a good, high volume air compressor) is OK for small parts . Big sheet metal pieces really need to be chemically stripped (messy) or professionally blast-stripped with soda or dry ice. "Ya pays yer money, and ya takes yer choice!"
Jerry
