GT Edge

Good practice is to clearcoat the frame with a direct adhesion clear in place of a primer.
This will maintain the finish of the raw metal and protect it etc

Then, you can fade front-to-back... you'll get a better fade with a candy or something with translucency rather than a solid or metallic.

Then you clear over the whole lot.

I'll bore you more if you've more questions.

There's a decent example of it here...

https://www.instagram.com/p/CiChDrosyaq/