I have been weathering a J25 scratch built many, many years ago by Mike Edge. The "real" loco was loaned to the Derwent Valley Railway (DVR) in Yorkshire - this one is owned by someone who has a model of part of the DVR and is pictured in the new book on the DVR.

It has been washed over with a mix of black ink and water followed by a dusting of black weathering powder for the body of the loco and tender and a brown/black mix around the lower part of the chassis and wheels.

Detailing was then added using black powder added to wet ink on the loco

and as shown in close up

.

Along the bottom of the tender tank a similar approach has been used - and a bit of "rust" added around the tender tank filler

Ant questions - feel free to ask