Has anyone experienced paint going on grainy, heavy, and taking on a light grey haze on the surface. using Model Masters enamel paint with Testor's thinner through the air brush with about a 60/40 thinner to paint ratio. I have been using this paint for 30 years and have never seen this before. Anyone have any ideas?

Is this happening, with several paints or just one? If it is just one, you may have a bad batch or the paint may have gone bad. Usually, grainy means that there is not enough thinner. I would try 7:4, thinner:paint or it is too dry. You can add a drop or two of Windex, as a flow improver.

Joe,

Could be a bad batch of paint....increase the thinner to paint ratio as suggested...test with another color but

DO NOT ADD WINDEX TO THE MIX

Windex contains water and alcohol and you are using enamels...you'll end up
with quite a mess as the two don't mix.

Cheers,
Joe

Completely forgot the use of enamels. I'm used to acrylics.

Without more details, this to me sounds like insufficiently diluted paint. The gray haze on the surface sounds like the paint is drying in the air slightly before it reaches the surface and is creating more texture, and hence a cloudier surface. Are you noticing any orange peel on the surface? Are you using a moisture trap?

And, as stated above, windex is not for enamels. The ammonia tncontains is good for lifting acrylics but not for enamels.

Had the paint been sitting awhile so that the pigment settled out to the bottom? The carrier liquid can also separate. I've had this happen to me with model master paint that had separated and sat for a while and I didn't mix it thoroughly before use. This is when I bought my first Robarts shaker and started using small, clean pieces of gravel for agitators. Several minutes of shaking and proper thinning fixed the problem.

Here's what I think-- I've used MM enamels for years too. If the paint was properly diluted (60/40 is a pretty good mix, as you have said), you may have some old paint where the carrier has separated from the pigment. I've noticed this happens to Testors paints (MM is a Testors product) when they age, especially if they've been subjected to high or low temps for a long period of time. Sometimes this separation of carrier will cause that "gray haze" you're speaking of, while the separated pigment causes a rough, grainy or "orange peel" surface. Try a new bottle of paint. I don't think it's your AB from your description of the "haze". You might have some luck using lacquer thinner in restoring the paint for airbrushing, but I'd do a test shot before applying it to a model. I occasionally thin and airbrush MM with lacquers when I want a fast drying super flat finish.
VR, Russ

How's the weather there? If it's been overly-cold, as it has been here, and if you use electric heating, that will dry the house air having an adverse effect on airbrushing. Conversely, so will humid environments.

Thanks for all of the great input. I forgot to mention that my current location is Brisbane, Australia. I moved from the US 3 years ago which certainly makes a difference with this issue as it was 85 degrees Fahrenheit with 60% humidity. I think that the issue is an extreme case of the paint drying before it reached the surface of the model. I might try switching to white spirits for a thinner as that does not dry as fast and increase the amount added to the mix. Over the years I have used Model Masters paint that I had on my shelf from 5 to 8 years that had separated, yet never had this problem. This Paint is only 2 years old and just opened so I don't feel that paint age or pigment separation was the cause. I am use to painting in Ohio and not Queensland, big difference.

Sounds like water in the paint to me. Light grey haze is the water trapped in the paint as it dries. Check you compressor and if you do not have one get a water trap. Are you using the airbrush thinner from testors or just the normal stuff. I have never had much luck with the normal stuff but like the airbrush thinner.