I picked this up at Warley plus some discounted Hornby weathering powders (one is a fetching shade of pink!).
It's got some interesting articles on rolling stock. I've been struggling to weather a steam loco and this gave me some food for thought.
http://www.pdfmagaz.in/01010113-hornby-magazine-skills-guide-weathering-volume-one/
https://shop.keypublishing.com/product/View/productCode/SPEC30
Kathy