I needed to etch a brass tag and needed a resist. I tried about 4 kinds of spray paint but they all left behind a film that made the ferric chloride etch inconsistently. I also tried polyester packaging tape but that did not burn off cleanly either. Finally, with deadline looming, I just used some blue painters tape. I thought it might hold up for at least a shallow etch. In reality it worked great!
Here is the finished product, a custom post-it note caddy.