Dewen, one of ML crew had posted these tips in our club section and I thought it was worth passing on.
After seeing a nice start on painting my Flyrant, a gamer asked me the other day to give him some tips on airbrushing with regular paints. He has a gravity fed airbrush. I sent him this.
1. I know the pros use Vallejo, PPP, and GW paints. I do not recommend using metallic paints unless you purchase metallic paint for airbrushes. I highly recommend Vallejo Model Air for metallic paint. I have used them and they are fantastic.
2.I thin my paints and clean my airbrush with a mixture of 15% rubbing alcohol to 85% distilled water. Buy the most concentrated rubbing alcohol you can (90%+). Some of the stuff on the shelves is only 70%+. If you can only find the less concentrated, add less water in the mixture to get desired concentration.
3.Optional: You can also add drying retarder to help slow the drying process, which decreases the likelihood of some fast drying paints jamming your airbrush. I know a red that I use for my blood angels tends to dry faster than my other colors. With experience you get used to which paints need the drying retarder. I would not get to concerned with the drying retarder in the beginning. I mention it in case you notice. I use Slow-Dri by Liquitex. You can find it at Michael's, Hobby Lobby, and art supply stores.
4.The rule of thumb is 5 part mixture to 1 part paint, but it depends on the paint you are using. Brands vary and the age of the paint can also effect the thickness. I mix mine in a plastic cup. Stir - do not shake the paint and mixture. Shaking adds creates air bubbles.
5.Keep cotton swabs (aka QTips) around your painting station. They are handy for cleaning deep in the paint well after rinsing and changing colors. Cotton swabs are also useful for wiping the nozzle.
Keep your needle clean. While painting, check the needle tip to see if dry paint is accumulating.
6.You can purchase cleaning kits that have tiny brushes for thorough cleanings.