Thanks to Reckon for his knowledge on this subject. These are all his words.
It's basically this: (I'll use a Norton I just completed as an example)
A paint job with leafing will need to be looked after, washed often and waxed often, sometimes the design will shift under the clear (sizing applied too thick, and not let dry before clear coating) and the clear will need to be re-applied after about 5 years if left outside in the sun, but garage cars and bikes will last better than 15 years if cared for (now you know why those firemen are forever waxing those trucks)
That's all there is to it, and it looks simply amazing under 3 coats of urethane clear, in direct sunlight.
The newer "faux" leafing materials (composite, usually aluminum, anodized, or tinted, varigated, etc.) are a lot less expensive to learn on, and are JUST as fragile as the real deal, so practicing with the cheap stuff gets you comfortable faster, so practice on the cheap stuff before you paint that f-350 fire engine red, and start with the scroll work.