The upper surfaces of this steam locomotive are shown with a heavy layer of soot-based grime. This is achieved by adding more weathered black to the mixture with frame dirt. If you look at the attached photograph you will see the difference between the wheels and the cab roof, for example, but I doubt (hope?) that you will see the join. By gradually changing the proportion of black and brown in the mixture, as work progresses upwards, the chance of 'tiger stripes' is significantly reduced.

Once the dark mixture is applied the brushing downwards process begins yet again. One obstacle around the boiler is the handrail, which prevents a smooth movement from the top to the bottom of the curve. I almost overcome this by pushing the brush bristles down into the gap 'twixt rail and boiler and dragging upwards before starting at the top and dragging downwards. This method is then repeated from the handrail downwards. Not perfect, but it does produce random streaking and uneven patches.

The dark mix is also applied to the top of the tender in preparation for the rust and water that are to follow, being careful to avoid the real coal that has been placed therein.