Airbrushed Guitars and Helmets are a couple of things that make a lot of airbrush artists cringe. It's a very precise procedure to disassemble, prep and make ready a product to airbrush. There's the curved surface that doesn't want to cooperate with masking materials sometimes and the glass smooth finish to be restored before reassembly. Then there's the shear time involved, especially for guitars. If it is a guitar, your paint formulation can't decrease sustain properties or electronic resonance but still, like a helmet, has to be indestructable. Although there are some artists out there getting thousands for guitars, motorcyle tanks and helmets. Still... I'll leave it up to them to carry on the fine tradition.
Any other Item is fair game if you prep the surface correctly. Wood, leather, vinyl, metal can all be lightly scuffed with either 300-400 grit sandpaper or a ScotchBrite pad. Many products are availble to spray or brush on for prep, you can even get sprayable chalkboard in a can! No matter what your working on -ALWAYS wear a respirator.