is it drying in the cup or in the nozzel? if its drying in the nozel, from what ive learned, the air pressure may be too high. the amount of air coming out may be drying the paint on the needle and may also cause a grainy finish

I spray at about 15-20psi for MM acryls and have never had a problem

I use distilled water at about 60:40 water:paint and do several light coats. Maybe you just got a bad jar?

Hi Rob:

Like you, I have always had problems with MM Acryl paints drying on the airbrush nozzle or clogging and then spattering, etc. I had the most luck using windshield washer fluid, but even then, it was inconsistent. So, I ended up just giving up on MM and switching entirely to Tamiya for airbrushing. I still use my MM Acryls for brush painting, at least until they are used up. Now, whenever I need to replace or add a color for brush painting, I buy Vallejo.

I know this is not the answer you are looking for, but maybe it is time to make the switch to something new?

I've had mixed results with MM acrylics in a Testor/Aztec airbrush myself. Just a few observations on what others have suggested.

First of all, what is the relative humidity? Hard to believe, but I've been able to paint with MM acrylics on very hot humid days in the middle of summer in my garage. On dry, winter days, I tend to have clogging issues.

How old are the paints? Not just when you bought them at the hobby shop since unfortunately, some paints gather dust at the hobby shops and can start to go bad. I had one that I tried to paint with this winter that gave me fits. I bought a new bottle and had no further issues. The thing literally was drying rock hard within seconds of starting spraying. The initial spraying quickly became spattered and such just before it dried out.

What nozzle are you using? Testor/Aztec made special acrylic nozzles that are slightly different and tend to clog less.

What are you using to clean your airbrush? I swear I've had residue from switching back and forth from acrylics that caused be fits between the paints. I try begin each airbrush session by spraying some solvent/thinner through the clean airbrush just to be on the safe side.

Finally what are you using as a retarder and how old is it? With the right stuff you should be okay. At one time I had original MM acryls (talk about difficult) and their reformulated versions. The associated thinner/reducers were not compatible at all, but I honestly didn't know they had a retarder formulated for them. Guess my now-defunct local hobby shop never carried it and I never considered it.

Rob;

I've used MM acryls several times and found them mostly pretty pleasing. I DID find that they like being thinned - usually I go closer to 2 parts 35% isopropyl alcohol (the cheap 70% split w/ distilled water) to 1 part really well-mixed paint. I generally shoot at around 15 psi - less when doing small areas - so maybe MM likes lower pressures, too. The relative humidity and temperature do matter - I try to paint when it is cooler and when it is a little moister / more humid.

I did get some clogging in my Iwata HPCS w/ 0.5mm needle... I found that I could avoid this issue almost entirely by finishing-off a spray-stint or pass with "spraying" a blast of air to clear paint off the AB tip. That, and occasionally I dip the AB nozzle into a small cup of alcohol and swirl it around, and follow with a blast of air...

Maybe this would help in your case?

Bob