Reaper now makes both a white and a black brush on primer. I\'ve been using the white almost exclusively for my priming needs for at least a year now and the only problem I\'ve had was with this last mini I painted. It was primed with the dregs of a bottle and I don\'t think the mix of thinner to primer was right. I spot primed with a new bottle and it was as good as usual. It sticks pretty well, I usually have a bit of a time cleaning it off a ceramic palette, even with soaking. That\'s the Master Series primer in the dropper bottles. They also have a Pro Paint primer in a twist off cap. It\'s decent, but Reaper themselves say it\'s not as good as the Master Series.
Before Reaper came out with the black I had also used Derivan black primer. It was _very_ thick (though not clumpy or anything) in the bottle I purchased, not sure if that\'s standard or it was on the shelf for a while, but it thinned down beautifully and worked fine. I imagine they also do a white primer, but I don\'t know for sure.