I'm doing SPI single stage black/black. It's among the darkest & for black the ss can look darker with the color up into the clear mixture, as opposed to just under it.
Don Hutton, which I know from pro-touring & spi forums has won awards on several ss black jobs for the same customer.
Spi epoxy builds strength with thickness & is a great start. Also great thinned down as a sealer/bonder just before paint. Plenty of info on spi forums.
I also see Don started using the new 3-m trizact , which jumps from 3000 to 8000 grit in 1 step. I got some & never tried yet as I haven't worked on my own schtuff in a year & a half, but it seems well liked.
And a ton of SPI epoxy on those bumpers... Don
www.spiuserforum.com
I can't twist anyone's arm as far as what to use, but I can make you drool with examples. Any great product can give you a similar result, using each particular product correctly & mind boggling hours of labor of coating & block sanding various materials on a straight as possible surface can't be skimped on. I prefer a black paint job that makes you smile without waving back at ya.