'Donn Yost' airbrush technique

My biggest modeling discovery of 2021 was the 'Donn Yost' airbrush technique. For 25 years, I'd been trying to spray gloss enamel paint from Humbrol, Revell, and other brands without getting orange peel or drips. And I never really succeeded, which is why I've never airbrushed a car model body. I knew the problem was largely with the airbrush: it atomizes the paint very finely, too finely, in fact.

Droplet size theory

Allow me get technical for a moment: the smaller the paint droplets created by the airbrush, the greater their total surface area, and the more thinner evaporates during its few centimeters of travel from the airbrush to the model. I dare say that in most cases, all the thinner that you added is gone before the paint reaches the model. And I think some of the thinner in the paint itself has also evaporated. As a result, the paint arrives thicker (more viscous) on the model than it was in the tinlet! And that prevents the paint from spreading smoothly. That's why I'd been searching for years for an airbrush that atomized less finely, but unfortunately, I couldn't find one.

I'll spare you the calculations, but every time the droplet size halves, the total area of the droplets doubles, and (roughly) evaporation doubles. But the great unknown is what size the droplets actually are. Maybe this can be established with high-speed photography? I gave it a try with my pretty normal equipment (Nikon D90), but even at 1/4000 second shutter speed, the spray moves too fast to capture it.

Breakthrough video

In 2021, I saw this video: Paasche H airbrush - The scale model workhorse !. The modeler in the video sprayed a super-smooth car body in one go, following the 'Donn Yost' method. The recipe: a Paasche H airbrush and a 1:1 dilution with lacquer thinner. I immediately understood why the Paasche H was so important: it's a rather primitive airbrush that atomizes coarsely. I ordered one straight away.

Paasche H airbrush

This is the Paasche H set that ordered for 60 euros. I made one small modification to mine: I painted two stripes on the nozzle, so I could see how many turns I made. For the final paint layers, you really have to open up the nozzle. It requires 1.5 to 2 full turns, giving a paint flow comparable to a spray can. That surely takes some getting used to, if you come from working with a 'normal' airbrush. Paint consumption is also much higher, of course, so prepare enough paint! Another aspect is whether your spray booth can keep up - mine can't.

Experiments

I tried a random Humbrol color (H68 Purple) on some Monogram F-84F scrap parts, and indeed, it worked perfectly. No drips, no orange peel, but a mirror-like shine - Eureka!

I did more experiments, and the technique worked with all the enamel brands I own: Humbrol, Revell, Model Master, and Xtracolor.