I used Testors airbrush thinner. I only use that when I airbrush & its pretty old. Does this stuff get bad over time? I use good ole Walmart thinner when brush painting & that can take some time to dry as well, but nothing like the airbrushed paint job. And I certainly agree with you on the Testors inconsistant consitancy! Thats all they carry at the local hobby shop & Hobby Lobby, beside Valero acrylics. I have finally found an online store selling Humbrol, which has been good paint in the past, tho I've heard they've changed their formula. I want to give Tamiya a try too. I have been impressed with their primer, smoke tint sprays & masking tape.