Here is the result of the weathering of my RH Little John and a rake of gravel wagons.
And here is the way I did it. Thanks to all the good advises is this tread.
First a thinn coat of matt varnish, then a wash of black and rust colors mixed with white spirit.
The rusty chimney and the footstep are drybrushed with burnt sienna powder color. Inside the cab a woodenplank floor.
The roof is first painted in different rust colors, then a layer of chipping fluid, and a topcoat of silver acrylic paint.
When the acrylic was dry, the roof was dampened with water and scratches made to look like rust spots.
Then some ruststeaks and some soot from the chimney.
Finally the little beast was given a matt varnish to seal the weathering.
Those gravel wagons were also weathered in the same way as the roof of the engine:
First painted in different rust colors, then a layer of chipping fluid, and a topcoat of grey acrylic paint. When the acrylic was dry,
the wagons were dampened with water and scratches made to look like rust spots.
Finally ruststreaks and a topcoat with matt varnish to seal the weathering.