When using non gradeproof materials, what kind of protective film do you use to put on your material before cutting/engraving?
Ah, the term you’re looking for is “masking”.
Lots of discussion on the forum about it, here’s a post you might like. Check out #2 in particular:
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I have a roll (Amazon) of this for those times when I feel like masking something:
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So much good info about masking in the forum, but I also want to mention that your don’t have to mask everything. It’s fine if you want to, but I’ve talked to a few people who thought it was a necessity, so I mention it now just in case.
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I’ve had a roll of 12x300’ masking for a few years now. 
I’ve got about 1/3rd of the roll left. A bit out of the shelf life, but still works good!
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