This step give the pre-final effect of burned out surface. I didn't use this technique before, that's way tested it earlier on old tank model to try all possibilites.
Firstly, I applied Heavy Chipping Acrylic Fluid by airbrush on main burned out sheets. Two or three thin layers is enough. Then I had to wait above 5 minutes to allow layer get dry.
The next step is applying black color. I used Humbrol Enamel H33, which was forgoten by me, because I didn't open it by ages.
In the beginning, I airbrushed few turret sheets The paint was diuluted by original Humbrol thinner.
After one or two minutes, I've started removing the humbrol coat with water. I humidify the coat very soften using flat brush, which was moisturized by water. After a while the coat started removing from the previous surface. It's important to control the quantity of chipping, which we would like to get.
When I finished the turret, I started paint the rest surfaces on the tank in the same technique.
I'm not satisfied in 100% of the final effect. In my opinion, I diuluted Humbrol enamel to much and the layers were too thin. As people say...pratice makes perfect.