Lamp masks, window frames, spoiler frame parts etc. I put on the scanner first to keep 1:1 patterns from them for repeated if necessary use.
Black frames are best printed on clear decal sheet, only cut out at the outline, placed where needed, let dry for two, three hours ( trial ) and then with a really sharp scalpel or hobby knife cot out the inside. After this short drying time normaly it is still easily to be peeled off. The glue residues can be removed with a wet paper towel. No pressure with the blade on the glass part - if it is really sharp, it "falls" through the decal carrier.
Roland