After searching at least 10 books for usable photographs I have managed to find a few that allow me to establish which parts of a cared for locomotive are cleaner than the rest. I thought that Gordon Edgar's wonderful books would help, but subsequently realised that a lot of the photographs that might have helped were re-touched black and white ones. Note that this is not a criticism! I have found many other photographs of small industrial locomotives that have provided clues about colour and placing of oil, grease, dirt and more, so I can make a start on the dirtying process.
I have decided not to make any more changes to the locomotive before starting on it. Many things could be tweaked, replaced, added or subtracted to improve it, but this is not intended to be anything other than a weathering exercise.
My plan, such as it is, is to produce an oily but fairly clean chassis and wheels, topped by a dirty running plate and cleaned tank sides, cab sides and bunker. The smokebox will be finished matt as befits a hot but maintained one, and the upper surfaces will be sooty. I will attempt to work on the cab interior as well, but that will be a little tricky because of the rather small openings.