I have read about it in some trade mags, but if anyone knows, these guys would.
It's the powder coating forum at Caswell.
I don't follow it, but it has helped me in the past, especially when I was just starting out.
Caswell, Columbia, and Pendry are the three places I have bought from before. All good service and good powders.
If you do find the answer, please post back here. Thanks.