as many answers as you get, you’ll likely find you have that many different opinions.
Logically speaking, any area or surface that is not clean dry bare metal is going to provide a surface for blast media to stick to or hide in. Thus, you need to clean the castings out thoroughly before using any sort of media on them. I’ve glass beaded countless cylinders over the years and they get cleaned out thoroughly before AND after. I don’t use sand, only glass. Haven’t tried walnut shells but I hear some folks prefer that as opposed to glass. The trick for me is to get rid of any oil or carbon residue before it goes into the cabinet. That means either cooking or burning the crap out, or using oven cleaner to dissolve the tough stuff. The other thing I do is use a series of brushes with a mix of hot water and laundry detergent to scrub blasted parts out. The brushes I use also work on your trumpet or trombone if you ever want to scrub the tubing out. Scrubbing with laundry soap and water will remove any residue from blasting (or honing if you break the glaze on the cylinder walls) but also creates the opportunity for flash rusting of bare metal surfaces as the part dries, so be ready for that.
Hope this helps.
Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...
