I haven't heard of the purity seal stuff, but it sounds kind of Space Marines kinky to me. image

No, there is a simple matte spray that comes in a black can. I think it just says Matte Varnish on it. Not 100% sure. But it seems to do pretty fine by my terrains, and I use a lot of flock, so I thought it might help you, as well.

Thing about it is, make sure to clean it really well after use and to use it up in relatively short time. I busted it out yesterday after it had sat for awhile, and found it gummed up and spraying wet. Sucks, because it's so much more useful to me than their primer.