Fesan
the acrylics thin with alcohol right? And whats this retarder you speak of?
Now I'm confused. From a previous post, I was comfortable that you were using the right products with your Vallejo acrylics. Now I'm not so sure.
You don't want to use anything except Vallejo Airbrush Thinner and Vallejo Flow Improver. At least for now, as OMG said. And also, and OMG said, get near alcohol and be prepared for a complete airbrush teardown and a horrible, goopy mess.
If you throw anything in the mix that didn't come out of a Vallejo-labled bottle, that throws variables into this thing making it pretty hard to sort out. And Vallejo has so many confusing products, you can even get into trouble mixing Vallejo stuff with other Vallejo stuff sometimes. I have. (for example putting Vallejo Retarder Medium in an airbrush. Oops)