4 Let's add some rust! Add a new layer (Layers>New Raster Layer) Apply Clouds tube (refer to this link if your PSP doesn't have a clouds tube installed)
Tube Settings:
Tube = clouds
Scale = 100
PressCTRL+A to select all active objects on your current layer. Pick the Selection tool and click your mouse once anywhere on your image. The clouded portion should become the active selection.

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