“the old hardtail frames I have are monster solid and heavy. Thick wall tubes. No way that I would worry about blasting.
Guess the manufacturers changed to higher quality aluminium now?“
It’s not really about new Vs old, but type of frame and intended use etc.
Some of the older Alu frames (Cannondale CAAD4/5, Klein, Principia etc.) are pretty thin walled and it’s more about whether it’s a lightweight XC frame or a burlier kind of frame.
Tube manipulation techniques have changed and improved over time but the Aluminium grades/alloys used haven’t really changed much and tube wall thickness is mostly going to be dictated by type of frame and intended use, there are some specific areas and bits where it’s possible for things to be ‘a bit thinner’ than older frame, but that’s more about being able to control where the material is, but on average there’s not a huge difference between old vs new in terms of wall thickness, certainly not in terms of ‘old’ frames being safe to blast and ‘new’ frames not being safe. A light weight XC frame is still going to be thin walled and a burly trail or enduro frame is still going to be thicker.
Anyway, yes it can be OK, but depends on the specific media used and who’s doing it…