adobe photoshop - How do I get this uneven airbrush effect similar to old art deco posters?

This is an section from a poster made back in the 1920s or 1930s, that was made using an airbrush:

What interests me most is that it has a rough, spattered quality. It's as if the airbrush didn't work very well and sprayed unevenly, resulting in varying dot sizes where the paint landed.

I've tried to get this kind of effect with the airbrush tool in Photoshop, by manipulating scattering levels and trying various brushes. However, I can't quite get it.

However, when I've searched for Photoshop tutorials, anything under the term "spatter" is way more exaggerated than I need, and anything with a "vintage" or "grunge" level is about the overall style, not specific brush settings. At least, not that I've found.

How can I set my airbrush to get a gradient quality like the example picture, or something similarly uneven in quality?

This is a section of a poster from the movie The Rocketeer, which has a similar effect:

Answer

I started with two solid color layers - beige and red.

On the red layer I added a layer mask, filled the mask with black and then choose Filter > Noise > Add Noise

Then, unlink the mask to its layer and use free transform (Command/Ctrl-T) to scale the mask up so the noise becomes clumps.

Repeat the Noise filter, then scale mask a few times (on the same layer mask) to create a basic splatter of the red.

I then duplicated the red layer with it's mask and set up a brush......

The Dual Brush and Scattering dynamics can create a very good "splattering" brush effect. Combined with a tablet and pen pressure used to alter opacity dynamically, you can then just brush on areas where you want more splatter.

Finally I selected the portion of the image I did not want any splattering and filled the area on the layer masks with black.

Again, this is just the path I would pursue. It still needs some refinement but overall you can get some interesting thick airbrush splatter type effects this way. Combine it with the a few techniques for the first sample image and you can get both canvas grain and paint splattering.