This article describes the process of weathering passenger carriages.
Because they are in the forefront of service to the public, coaches are/were generally looked after to a much higher standard than most other items of rolling stock. Therefore, only a 'light dusting' weathering is generally appropriate.
The coaches in the pictures above have all had their under chassis painted in a track colour brown which is a mixture of Humbrol 113 Matt Rust and Humbrol 33 Matt Black. This finish is intended to represent track and brake dirt and it is important to distinguish this from the practice of the early 1970's where BR actually did paint under chassis brown for a few years as represented on the Airfix MKIId coaches.
The coaches in the picture have all had their wheels replaced with Romford, painted and have had bolsters (in the form of 10BA or 8BA screws) fitted on the bogie at one end:
Personally, I find nothing worse than wobbling rolling stock so I check wheel trueness and fit bolsters where necessary.
The photos also show how I fit Bachmann Ez-Mate buckeye couplings to this type of bogie on my coaches. The height is set at the Kaydee height gauge standard.
The collett coach has had black Carrs powder applied to the roof in a side-to-side motion (weather lands on the top and runs down the sides).
All of the coaches in the photos have had a limited amount of brown powder applied to the lower body side, working upwards, consistent with the 'plimsoll line' concept - photos will usually show this effect.
As indicated in the introduction to this series of articles, many RTR models these days have a paint finish which will not take Carrs powders because the finish is too smooth and/or shiney. This problem can be resolved by painting a model with a matt varnish prior to applying powders, although for coaches, I don't normally bother because the level of weathering necessary is so low that it doesn't really matter. Good working in with a stiff brush will help, but not too stiff such that the brush scratches the paintwork.