I have often been told not to.
I am not so sure though. I mean a final flat before applying the clear.
Should you flat metallic colour coats? (Ivor!)
Moderator: Moderators
STOP! 
Don't do it Al!
The idea of the basecoat is to provide a fast drying coat of colour which allows the metallic flakes to assume all different angles within the colour, thus reflecting the light randomly and providing that proper metallic sparkle.
If you flat the basecoat, you'll take all the tops off the flakes and kill the metallic...the same happened if you use a slow thinner in the basecoat, all the flakes settle out and it kills the metallic effect.
The clear gives you the gloss and durability, so by all means flat the primer and the clear but let the basecoat do its thing...man. 8)
Don't do it Al!
The idea of the basecoat is to provide a fast drying coat of colour which allows the metallic flakes to assume all different angles within the colour, thus reflecting the light randomly and providing that proper metallic sparkle.
If you flat the basecoat, you'll take all the tops off the flakes and kill the metallic...the same happened if you use a slow thinner in the basecoat, all the flakes settle out and it kills the metallic effect.
The clear gives you the gloss and durability, so by all means flat the primer and the clear but let the basecoat do its thing...man. 8)
