With metalizer no base coat is necessary, nor recommended by Testors. This is why I mask my colors twice and not just spray them, mask and cover the unwanted areas with metalizer. I did an experiment spraying over a gloss color and it didn't work. Spray right on bare plastic. Wait about ten minutes and buff it out. The more pressure you apply, the shinier it gets. (Look through my articles for my F-89 Scorpion, you'll see how much of a polished surface you can achieve.) Just be sure to introduce a fresh surface of the towel you're buffing with to the paint as the collected aluminum particles can eventually leave a gash in your finish. I'll post a picture of my B-57 later to show you what I'm talking about.
For different panel colors, I've found that despite Testors' instructions to the contrary, you can mask certain colors of metalizer. (I've done stainless steel, burnt metal, magnesium and burnt iron successfully.) I usually spray aluminum last after masking all these colors. On my scorpion I decided after polishing to add some shades to the upper wings to break them up a bit. For this masking is also easy (if you're using an airbrush). Cut some strips of paper about 2" wide and keep them in a bowl of water nearby. When you want to mask a panel, lay the strips around the perimeter, blot the water beads away with a towel and spray.
