In theatrical lighting, a gobo is a thin metal, plastic, or glass template that blocks light, allowing a pattern or image through. Like a slide in an old slide projector.
The issue is heat, which is usually too much for straight-up plastic.
Classic gobo’s are cut out of quite thin steel or other metal. Newer ones are cut onto glass. I’ve heard of acrylic being used with LED spots, but not sure if it’s a special type of plastic.
What materials could the GF cut that could be used as Gobos? I’ve heard how bad aluminum is, so aluminum foil’s out? Metal HVAC Tape? Really thin steel? Could it etch away a paint coating, but leave a clean surface below? Is there a cuttable acrylic that can handle high(er) temps?