George No offense to Bailey, but You said she gave the "Correct answer" She also said that Alcohol will not work. I really really think you are having some issues today, perhaps its your old age, or perhaps its the fact that you are a cranky old fart? Who knows Im not a doctor. But What you failed to miss was that the retarder and extenders CONTAINS ALCOHOL!!!! You also have a very well seasoned artist on here tell you that Alcohol does work. I have also spoke with many other artists who thin acrylics with alcohol to change its properties and to thin it. This isnt about How many Nyala anyone has mounted. This is about you and your constant need to be right. and when you happen to not be you get upset and extra cranky. Again I am no doctor so I will not analyze that issue either. The question again as you stated was How to thin Acrylics. and we answered it, but hey what the hell do I know. Im no doctor but I do have a BFA in Painting, drawing and sculpture. But we all know what you think of us college folks. Our degrees are as good as the paper you store next to the throne. In short Yes you can thin acrylics with alcohol and extenders.