To reiterate Andrew Stewarts comment, media blasting of such as 531 should be done cautiously. 531 tubing for
bicycles was in the 0.022 to 0.045" thickness range. Bike Tech magazine in the early '80s media blasted sheet
metal of various thicknesses (basically bike tubing) and measured before and after thickness with various media
and found that sharp sand (the most aggressive) could remove upto 0.006" of thickness. Since this removal
would be assymmetric the risk to the frame could be significant. Soft media only should be used for quality
frame paint removal.