Off-topic regarding insulators, but on-topic regarding cleaning complex-shaped light-gauge rusty steel work in electrical installations: looking at your picture in post #16, I'd suggest having a go at electrolytic rust removal:
https://www.vintage-radio.net/forum/...d.php?p=983016
It won't damage what you have, and it'll be a lot easier to clean up than attempting to do it by abrasion. Don't do it with any alloy, or anything painted where you hope to save the paint.
If you use a galv anode, you'll lightly zinc-plate the work piece - not sure if you'll get enough on to make it less inclined to rust! Probably best done outside wrt fumes, splashes etc.