Neil
What paint colours / mixtures did you use for the wheels and motion as shown on the Standard Class 4 image
Regards
Bob
I started blowing over the motion - by airbrush - a very thin, barely discernible layer of dirty grey-brown Bob.
Once this paint layer was dry and hard, I followed this by applying a mixture of oil paints.
Mainly Raw Sienna, with a little Burnt Umber added in, creating a consistency heavier than a wash, but not so thick as to fully colour the motion if that makes sense.
Here and there to create a more oily sheen I added some Windsor&Newton Liquin Original. The sheen it leaves is subtle, but I like it for scale models: I don’t like anything looking too glossy on models.
Hope that’s useful Bob.