I’ve successfully used aluminum foil to prevent flashback. That doesn’t introduce the extra flammability element of adding layers of flammable material with air space in between to encourage flames. 
Gorilla tape is my go-to for getting the masking off acrylic. When I was making the bazillion little pieces for my [Mastermind](http://Mastermind Game With Rack & Pinion Box Latching Mechanism) and Catan games, I’d lay out a strip of Gorilla tape, stick a bunch of masked cutouts onto it, give them a minute to adhere, and then peel them back off and do the other side. Still tedious, but you don’t risk the hazing you might see otherwise.