Flat black not smooth

Well, I sprayed the nose again today using the Testor's enamel thinner.  The results were better, but I still have splotches.  It's probably 1/3 bad as what I have pictured.  I may grab a new bottle of paint and give it another go.

Shorts wrote:

Quick question, what do you mean by "generic" thinner?

A thinner not sold by the paint manufacturer as being specific to their brand of paint.

Tamiya and Testors thinners, for example, are proprietary—made by the company specifically for use with their paints.

Isopropyl alcohol, water, mineral spirits, etc., are "generic." 

The layer at the bottom may result from:

1. Too much thinner
2. Incompatible thinner
3. Paint gone bad.

I always test a generic thinner for compatibility before using it—and I recheck when I open a new bottle. Formulations not only vary from color to color within a brand, they also vary over time, often quite rapidly (as in one production batch to the next.) 

Also, paints behave quite differently when brushed as opposed to being blown through the air. If you think about it, the physical differences in application are rather great. 

jhande wrote:

As you mentioned - there was a layer of black paint in the jar and when test spraying you had big spots of clear coming out. Obviously the paint and thinner did not mix.

Thanks Jim.  I said there were big spots that sprayed out, I should have said they were black spots.  But there was a layer at the bottom.

 The paint I guess...hmm, when did I buy that (<-- does that make it old enough??)  haha  Probably last year sometime.  As I said, this flat black paint and thinner worked fine on the tires I brushed painted as well as some other small parts.  This leads me to believe that it is not the compatibility, but the mixture. (and I'm willing to test that out to be sure, regardless of which way it works out).

At any rate I did pick up some Testor's enamel thinner in the bottle today.  I'll try that out later.

First thing, how old is your flat black? If it is getting old it will start giving you problems.
Second, was your paint to thinner ratio close for flat paint?

As I mention in my above post, just because the thinner worked fine with the white paint doesn't mean it will play nice with the flat black.

As you mentioned - there was a layer of black paint in the jar and when test spraying you had big spots of clear coming out. Obviously the paint and thinner did not mix. You should not have seen a layer of black paint in the mixing jar (I would have stopped there). When spraying, the clear water like spots was just thinner (and carrier agents) minus the paint pigments (color). For sure a not mixing together issue.

Use the hardware store mineral spirits to clean out your AB.
Use the few drops of recommended same brand thinner to reduce the paint.
At least until you practice and learn what paints are compatiable with what thinners.
I know it's a pain and cost more for the model brand thinner. But it will save you from ruining your kits until you have time to experiment with some paint. I've got a chart kicking around somewhere that I'm writing down what paints "need" the same brand thinner. So that way I don't waist my time next time at the spray table.

Good Luck! 

Thanks for the tips.  Thinner is Enamel (X-20)  I sprayed the entire top half with Testor's semi-gloss white with this mixture.  With the way the white turned out I'm not confident in that the problem is mixture incompatibility.

Probably a good piece of info that I overlooked was, when I mixed the thinner and paint in my jar, when I tilted the jar to check the consistency there was a layer of black on the bottom of the jar that did not sheet with the rest of the liquid.

 Also could be a sign, test spraying on my backboard I noticed with this black there were often big spots of fluid, similar to when you have water spraying out your airbrush along with the paint.  It was not a completely nice spray of mist. 

 Does this added information help the jury???  

 I'm going to the BX to pickup that thinner.  Testor's is the only brand they carry in the piddly model section.  I only go there to get things that aren't covered at the modeling store in town.  I'll try it out if the mixture thing just isn't working (Shorts <-- stubborn)

All very good recommendations and I would like to add my experiences with paint, especially Testors.

They seem to be a bit tricky when spraying with a generic thinner (such as hardware store mineral spirits), some colors will work just fine were others tend to leave less than favorable results. I'll first mix a small test batch and spray a plastic milk container so I don't ruin a model. If it looks nasty, I switch to Testors thinner.

Not all enamel paints from different companies (brands) use the same thinning agents, so it's usually best to use what is recommended by the company. Sometimes you can cheat though.

As far as using lacquer thinner with enamel paint... I know some folks do and claim no problems. But that was a painting rule no-no when I was spraying cars in the shop so I just can't consider that as an option. I mean, you don't spray lacquer over enamel so I sure ain't mixing the two together. But that's just me and my old schooling.

From Testors site -
If you are airbrushing Testor Enamels, use #8824 Enamel Airbrushing Thinner.
Use the following ratio as a starting point.
With Gloss; 3 parts paint to 2 parts thinner.
With Flat; 3 parts paint to 1 part thinner.

8824

Flat black paints are particularly prone to this sort of problem because the pigments are very fine and have a strong tendency to clump (the technical paint term is "floculate"—sounds like an obscenity, and to a paint technologist, it is!).

Very thorough mixing is required.

A compatibility problem can produce similar results. In fact, if you were using an acrylic thinner with an enamel paint, I'm surprised it looked this good!

Generally speaking, if you are going to use a proprietary thinner, use the one for the brand of paint you are using. While this is more critical with acrylics, it can be so for enamels, too.

If you want a generic thinner for enamels, use mineral spirits or naptha. 

Are you using Tamiya Acrylic thinner (X-20A) or enamel thinner (X-20)?

If you are using the acrylic thinner this will most likely be cause of the problem - acrylic thinner isn't compatible with enamel paints.

EDIT: PS. I'm not at all sure if Tamiya's enamel thinners are compatible with Testors paints. To me, Tamiya's enamels smell more like they are a lacquer based paint.