That has put me on the spot Alexander. I actually use Harder & Steenbeck brushes but would not have thought they were much different from Iawata as they are both good quality.
For the .2 nozzle.
Model Air try about 20% thin
Model try 50% though you may need more thinning. If you look at Model Air after thinning you need a similar consistency for the model.
Do not use a .3 or .5. But with a .4
Model air no thinning. Model I would go for 30%.
I use 20 PSI on the compressor.
These are rough figures & as said by Patrick practice & see the result. There are very many ifs & buts. Temperature etc. all make a difference & colour. Not the actual colour just consistency of the paint for some reason. Black, silver & steel in Model seem very thick.
Found once I had a bit of experience with practice you could gauge the thinner element.
You may already do the following but here goes. If your
airbrush is gravity fed then what I do is to pour in a little paint then the thinner then the rest of the paint as required. I then use a smallish brush to give the paint & thinner a rake around. Found if you put the thinner in first you can get a good squirt of thinner out first. Squirt on an old discarded plastic bottle to test before airbrushing on a model.
Laurie