Hi Nickg;
I meant to get back so here goes. 50-50 is Say 25 drops,(from the end of a paint brush handle. ) of thinner ,followed by 25 drops of paint in a Clean bottle. You don't want to mix it in the original bottle as you may need unthinned color for touch-ups later.
Over cleaned Plastic was mis-understood. The way I intended it to mean is to Clean the model Body, Hood, Trunk and Body accessories real well, Before painting. I use warm water and Dawn dish detergent. This stuff gets ALL the mold release and finger oils off the parts you have to paint. Rinse extremely well.
The trick here is that when air dried in an old cake dome, The parts will contain no impurities on the surface. Do not handle the parts after cleaning with bare fingers. At least get a pair of nice Women's dress gloves from the local Target. White Cotton, for sure.
Yes! you can get them at say, Wal-Mart, but I stopped buying stuff like that from there because of shorter than normal wear life! White cotton Gloves are used by even Museums to handle display Pieces. Because finger oils contaminate the object's surface.