Add a TAMIYA solvent to VALLEJO pigments to make paste.
And use this paste.

There is a solvent to fix the pigment in VALLEJO.
However, in Japan, Tamiya's solvent is very accessible, so I am using it.

You must not paint all surface with it.
Please add a little paint to surface few parts.

I use the writing brush for nails.
It is the cheap & disposable brush.(one Euro shop)
This writing brush is suitable for such a work.

At first, cover the base of the wheel.
And use the pigments paste.

Then, paint the surface of the side hull with the mud of the bright color.
Please do not paint evenly.

And make that dry.

Paint the surface of the side hull with the mud of the dark color.
It applies to the lower half of it.

Use the pigment as it is powder in this process.
It is not paste.

Drip several drops of solvents on the surface.
And sprinkle a pigments.

You must perform it quickly.
And you should not touch it.

After applying step 3, dry it.
The body is turned to the side and that's shaken gently.
Then, unnecessary pigments will fall.

So,the pigment turns to its original color as the solvent dries.
You must see the color of the dirt until it dries.

If you need dry dirt for a summer scene, the process is complete in this process.

Apply Tamiya acrylic smoke (clear color) to the bottom of the car body.
This is the expression of wet mud.

Smoke paint is absorbed by the pigment.
If the wet texture is not kept after the pigment dries, add smoke paint.

※ If you move a paint brush over a pigment, the pigment will peel off.
You must use smoke paint to drop water drops.

I use a medium color pigment of bright color and dark color painted on the side of the car body.

Pigments make the boundary between upper and lower color vague.
This is the same technique as in step 3.

After that, I added wheels.

Pigments fall out by touching with hands, so after all other work is over, add them to the wheels.

After the pigment on the surface of the wheel dries, rub the surface with a thin brush.
By this work, the pigment falls off the convex parts.

Machine oil soaked in mud is expressed by black of TAMIYA enamel