I use Bosny flat clear spray, some use Testor's Dull Coat. And yes, spray, there's also sealant for airbrush, and some acrylic sealant that you use with a normal brush.
regarding blotting...how do you guys apply it to a finished flesh tone??....once the blotted paint dries...do you then do a quick dry brush to soften the sharpness of the blot application?