Undercoating metallics?

I noticed that a gloss black undercoat made my aluminum paints lay down much smoother...

Until I built that F-86 a couple weeks ago, I'd never undercoated before, and I must say that the difference was rather surprising..

Much depends on which product line you use.

With my products it is not required. You also need to keep in mind that if you are building a model with fine recessed details, the more layers you apply in the painting process, the greater the chance you'll loose them.

I prime with aluminum (my paints of course )...start with with real metal just like the real aircraft.

 

It's sounds like something cool to try next time I do a metallic finish.

Metallics are essentially metallic particles suspended in a transparent/translucent binder/carrier (often it's this medium which is tinted to give them the required colour rather than the metallic particles themselves) and are often not entirely opaque (unless applied very heavily). I think that using a black undercoat simply provides a high-contrast backstop which emphasises a lighter metallic in the case of any "show through".