I always try to do multiple thin coats, I found that if I let each coat set up for an hour or so I can get 3 coats on and thats plenty. Paint it then set it down for a day, I put mine on top of the refridgerator, it keeps the kids away, its up high in the warm air, and I figure that the fridge fan must be circulating decent air. Also typically (for some reason..) darker colors take longer to dry, this was true in school with our oil paints too. I found the traps dried really quick, but it took one or two days before i was comfortable with the black. The pickling you see might be an incompatability with your base paint, what did you paint the helmet with (assuming you did and thats the pickling your seeing. Might need to let it cure and "off gas" longer.