Regardless of brand, I now always spray in humidity that is less than 70%. Temperature is a factor, too, so I strive for a temperature that is 65 to 75 degrees Fahrenheit. And the primer itself is a factor -- not only the brand, but the can temperature, its age, the amount left in the can, etc. And different brands have varying levels of sensitivity to environmental conditions.
So I've always wanted a side-by-side comparison of primer brands to guide me. As it turns out, I accumulated a variety of brands to try out, and I happened to have a large collection of recently assembled minis that needed priming. So, hey, I figured I'd try my own comparison and share my results with everyone.
So the four brands I tried are shown here:

The Armory can is standing in its cap, because the bottom dents and bellows out if you "shake vigorously" like I do. By the way, I shake primer for a minute and a half to two minutes before I start using it.
The Armory can had about 1/3 to 1/4 of its contents remaining. The other cans were brand new.
Note the nozzles. They make a difference in paint flow and diffusion. I'll speak more to that as we go along.
I tried my experiment in less than ideal conditions. The temperature was about 90 degrees. The weather report said that the humidity level was 45%, but I'm very skeptical that was the case. By the time I was done, I was sweating like a Malifaux Warpig. In any case, I tested the primers first on spare sprues to make sure the project was a "go", before I risked any valuable miniatures.
Going into this, I expected the Tamiya to be the best performer, based on comments I've read in forums. I looked forward to having a "go to", super-reliable brand when I just couldn't afford to fail, like priming my new Freebooter's Fate minis. The results surprised me, as it turns out. But I'm getting ahead of myself.
So here are the results of the sprue tests, in the same order as the cans are shown above. The paint may appear a little grainy, but that's only because the photos are so close up. From normal distance, the primers were more or less smooth. The speckly effect you're seeing is more indicative of general coverage and paint thickness.
The Army Painter primer shows very even coverage.
P3 goes on very light and thin. I could barely see it coloring the sprue when I started.
Tamiya shocked me. You can see where it pools around the letters. And the coverage was uneven. Parts of it heavy and parts of it light.
Armory showed even coverage, and you can see how differently the paint adheres around the lettering, not pooling at all and keeping the edges sharp. However, it seems to be the coarsest looking of the set.
OK, on to the cool stuff. Here are some of the test subjects, again shown in the same order as the cans are shown above.
I don't expect you to see too much difference in this group shot, but it is worth mentioning that the results are usable for all 4 brands. The devil is in the details....
After the sprue tests, I felt most comfortable with Army Painter. So that's what I used for my Freebooter's Fate minis. One word sums up using the Army Painter brand. Control. I felt like I had the right amount of coverage, not too thick and not too light. Light enough that I could lay down multiple layers if I needed too, as is recommended by many experts. The flow was not too light and not too strong, and the dispersal remained in a cone-size that was appropriate for the subjects' size. The pressure was even and reliable. The detail on the mini is preserved wonderfully. I am going to enjoy painting this figure!
The P3 paint flows from the can in a silky-smooth fashion that stands out from any spray can I've ever used. It screams quality. That said, though, it felt really weird to me. The coverage is extremely light, too light for my taste. And the dispersal is very wide and vertical. It probably helps in hitting the model at a variety of angles, but it probably wastes a bit of paint in overspray. Very interesting approach, and it shows that Privateer really cares about their product and about differentiating themselves in the market, but, unfortunately, it's not my cup of tea.
Tamiya flowed very fast. It pooled in the crevices of the model in an instant. It's a little glossier than the other brands, too. You can see drips on the side of the base. Yeah, maybe I could increase the distance at which I spray, but, next to the other brands, Tamiya gave me the least control.
Armory performs well, and it's good value. But it definitely demonstrates that you get what you pay for. The pressure was uneven (and I think that is independent of the fact that I was on the last third of the can), and the dispersal was slightly "cloudier" than the others. It lays down SOLID. You can definitely see what parts of the mini are covered and which parts aren't, as you go along! All in all, it's a respectable performer, but you can see that there's a touch of texture in the results. Good enough for army hordes in tabletop games, but not sufficient for display painting or tabletop centerpieces.
So there you have it. I hope you found this helpful. After I recover from inhaling all the fumes, I'll compare the hallucinatory effects between the brands!
Now on to painting. Yay!
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