Milani Nail Polishes

for the past few months i have been using the milani nail polish in black magic and i have noticed that after a few uses it starts getting a little chunky. i stopped using it for a few days and it started to get more liquid but it went back to chunky when i started to use it once again. i have been able to use it for dotting and for top layers but if i try to do it on the whole nail or i try to marble with it then it starts to go bad. for the price that these small polishes run i would want them to last a little more then they do. i have had NYC nail polishes last longer than these and the NYC only run for $1