The actual ratio you need will depend on your air pressure, and painting habits. A rough rule of thumb is about the consistency of milk. I spray Tamiya acrylics a lot and thin them 3:1 (paint:thinner), and I spray at about 15 psi.
The propellant cans are going to give you some problems, I’m afraid. They tend to get cold very quickly and this causes the air pressure to drop dramatically. You can help the problem by sitting your propellant can in a bowl of warm water so it won’t get as cold. You’ll probably want to consider a compressor or air tank pretty soon.
Loylein, try 1:1 as a starting point. That’s what I normally use with Tamiya but I use about 15 PSI pressure to spray. With a propellant can I don’t know what pressure you would be getting, if it’s very high you might not need to thin at all. You may need to experiment a bit as pressure and paint viscosity (thinning ratio) are linked.
When using a propellant can as an air source, make sure you firmly attach your model to the workbench or the air blast will blow it right off the table.
If you’re going to do more models in the future, I would recommend that you get a decent compressor, preferably one with an air tank. That propellant can (you didn’t indicate the size) will only last for a couple of models, and that would be stretching it. If you’re just going to build casually, though, then propel cans may be the more viable choice. Is this your first try at airbrushing?
I have found that a good way to get the right ratio is to open a new bottle and pour in thinner until it comes to a little under the rim of the jar. This usually works for me but it is sometimes a little thin.
Another method I use is to add a bit of thinner then stir the paint with a toothpick. then I pull the toothpick out and if there is a thick coating of paint on the TP I add more thinner. But if the paint looks translucent I have thinned it to much. I know I have the right consistency when the paint is covers the TP and looks thin on the TP.
I spray at about 15-20 psi.
Just experiment until you get a method thats works for you. hope this helps.
Airbrushing is not something that very many people master immediately; some, but not many. For most of us it takes a lot of practice to get decent and a lot more to get good. Get some styrene sheet, some inexpensive paint, another can of propellant and just paint anything. Paint dots and try to get them to line up and all be the same size (not as easy as it sounds), paint straight lines or circles and try to make them smooth and even, paint your name. Paint a square shape and then try to fill it in evenly. It doesn’t matter what you paint as long as you are getting the feel for your airbrush and what it’s capabilities and limitations are. You need to find a comfortable way to hold the airbrush so that your hand isn’t strained (straining will make your hand shake), and how to keep your hand still.
One critical word of advice … any time paint is spraying your hand MUST be moving. This means that your hand is moving BEFORE you press the trigger and is still moving AFTER you release the trigger. If you stop you’ll get a blob there. It isn’t uncommon to see lines that look something like:
0=========0
The dot at each end is caused because the brush wasn’t moving. On longer lines you may see something like:
0========0========0========0
Again, the blobs are where your hand stopped while you were shifting it. It takes practice!