Thanks Sean,
The tracks are easy, I first paint them in a metal base colour, in this instance Gunmetal with a bit of medium grey to 'calm down' the brightness. After that I gave the whole track a wash of Burnt Umber oilpaint. Then I made a runny paste of rust coloured pigments, and brushed that quite liberaly all over the tracks. At this point panic may set in as the effect looks to have severly backfired...

. The trick is to leave the mess to dry well, and to brush off the excess with a stiff brush. This will leave a build up of the pigments in the nooks and crannies exactly where you want it. At this stage the tracks look like the have spend three months out in the rain..

:-) . Final step is to use brown and yellow pigments to tone down the colour of the track. I brush them on dry, using quite a bit of pressure.
Cheers
Henk