The image in the last post of Oliviers Alfa is stunning. I have never quite got the hang of 'weathering', but did do what was obviously a good model of a BR 9F at Barry scapyard, as it fetched a fair few pounds when I cleared house prior to a move some years ago.
I will certainly try again when time permits. I am told it is a base coat, including top-colour in acrylic, with weathering in enamel, which can then be removed if problems have occurred. Looking at 'general' weathered finishes, an airbrush has to be a 'must'.