Weathering has been the subject of many books and articles in the past, it is seen by some as a black art, enjoyed by others, and many myths also perpetuated (such as you can only do it an airbrush!) There are various different methods and materials that can be used and many are as just as effective as others. I first put online via RMweb many moons ago my own methods, which then formed the basis of an article in the October 2008 issue of Hornby Magazine and now a version can found online in the Model Railway Features section of British Railway Modelling Magazine’s website Model Railways Live
The staged method that I devised over time, practice and observation is broken down into stages which I hope makes it simple for others to have a go and try. I stress that it is only my approach and there are many others. None of them, either the methods or the materials used, are either the only way or right or wrong.
However first and foremost the most important stage whatever the method being used is to research and seek photographs of the effect that you are looking for from the real thing, rather than using your imagination or copying someone else’s interpretation on a model as the finished effect will be so much better. At the end of the day have a go, practice on something simple, costs effective such a box wagon to start with and go from there. At the end of the day it’s both fun and rewarding.