It's the turn of the airbrush now. The inderframe will be discoloured using Railmatch Sleeper Grime, applied with an Iwata Eclipse SBS. The driven wheels are turned while the paint is sprayed, to prevent there being a patchy finish to the rims. With N Gauge and OO/HO Gauge engines this can be done with a PP9 battery, but this doesn't work with O Gauge. I use two pieces of scrap OO Gauge rail screwed into place through a piece of wiring terminal block set at the width of the wheel treads and bent to the width of the battery terminals on the other side.
The wheels are airbrushed first and then the rest of the underparts, not forgetting the buffer beams.
The wheels on the trailing axle are turned by hand. After I thought I had finished I saw from the photographs that I was wrong. I had to return to the spray booth and finish off the patchy bits I thought I had avoided!