I'm hesitant to chime in here since I'm not exactly a fan of swirls nor did I really know what a 'swirl' was before discovering this site AND to top it off, I don't even have the slightest clue about painting objects like guitars, cars, etc.
But Guru, just an observation here. If you're trying to go for a standard swirl, ones like Darren Johansen does, I noticed something while watching that UV77MC reissue video:
If it doesn't look good on the surface of the water - don't dip anything into it
I have to agree with this one.
In the vat Darren used, the paint on the surface looked EXACTLY like the finished swirl. He moved the guitar body around for the swirl effect, but the paint on the surface already had well-defined boundaries between different colors. Even on the surface of the vat, colors were not bleeding into each other.
When you look at the vat and then look at the finished swirl, you can obviously see how making sure the paint on the surface has a huge effect on the swirl. In fact, in casual observation I'd say it is THE most important thing. If the paint on the surface already looks bad, the swirl isn't going to look right.
I may not paint anything, but I am very good at figuring things out intuitively. My guess would be that this preparation of the colors in the vat is one of those things painters figure out for themselves but just never bother to document or perhaps purposefully keep to themselves as a trade secret.
I'd say that if you can perfect the process of setting up the paint in the vat, you've probably got about 90% of the entire thing perfected.