I use Sally Hansen's Hard as Nails. It always starts to get thick by the bottom. I have three bottles going at all times. A new one that's really thin, a half or less bottle that's thicker, and a thick one. I don't use the real thick one much, but there are things I need the #2 bottle for pretty often. When the thin bottle gets thicker I rotate them down the list one and toss #3 in the trash. I gave up on trying to thin them or make it all the way to the bottom. If there's a trick to revive them I have no idea what it would be.