Found the recommended grit is best after all.
I have been using the baking soda technique in my Badger mini sandblaster to get a nice grey finish on those difficult Delrin sideframes (btw the self-etching primer did not stick on the Delrin at all), The baking soda works, alright. But I kept having clogging problems despite using very dry soda and two moisture traps on the air line. It just wouldn’t flow freely after about a minute or two. Once it started clogging, it was game over for the day.
However, I switched to the recommended aluminum oxide 220 grit for the Badger tool. I had avoided this as it is well-advised to keep it away from any motors.
It works best, by far. It works faster and gives a better grey patina. It also seems heavier and less prone to flying around in the air, and because it works faster, there is less used overall. It is less prone to reacting with humidity, but I keep it in a sealed paint pail with a 1 lb. bag of silica desiccant that I got online awhile back.
I am weathering only sideframes or parts completely removed from any loco or car. I take them out of my “clean room” to the sandblasting area outdoors and then wash the items afterward carefully. I won’t let the aluminum oxide anywhere near the clean room… I change clothes, remove shoes, vacuum, shower, all that stuff.
I read up on the hazard data sheet for the stuff, and it is quite safe personally and environmentally http://www.sisweb.com/referenc/articles/alx.htm as long as I use the goggles and mask, which I have to use for baking soda anyway.
One problem was a source of the aluminum oxide. The closest hobby source was the shop in Ontario which sold me the Badger miniblaster. However, 5&nbs