Hey, now that you have posted a very good photo up close of the car in question, I can see what may be a problem. If I were you, I would use some type of dull coat...Perhaps Testors Dullcote. I apply mine with an airbrush and because it doesn't have to be precise, any cheap airbrush can do it. Anyways, everything sticks well to dullcote, to include pastels, your acrylic paints...Oil based artist paints are very nice too! On the other hand, realize that you MUST be working in a virtually dust free environment when you dullcote some thing. If dust or hair or anything gets onto it, it will be permanent! Dullcote the car and use a VERY fine brush...That should solve the problem of not being able to make smaller rust patches. Also, thin your paints... Not too sure what to use with acrylics, (water???) but with oil based paints you can dilute it down to almost a water like consistency. By dabbing it on little by little you can make for dramatic effects. Try not to smear the paint also... Use your fine brush to make streaks after you have allowed the paint to dry slightly...Should only take about 30 seconds if you are doing it correctly. And one last thing, be sparing with rust! I know you are practicing (which looks GREAT!!!) but on you real cars, be careful as to how bad you want them to look. The darker you rust is in the middle of the patch, the longer it has been unattended to...It seems as if mostly boxcars and gondolas mostly only get to the worst level. If you need anymore help, let me know! You're getting real good! Keep it up!
-Rich
