Good day,
Here are two links to a tutorial on weathering with coloured pencils. It's a very good additional way to add various types of weathering to your models...and is quite correctable/ reversable if you don't like the results. By the way...the article and the video refer to using window-cleaner....he is referring to the blue ammonia based US window cleaner called Windex.....I believe Windolene has a similar product on that side of the pond....if not...plain water works just as well.
http://model-railroad-hobbyist.com/magazine/mrh-2011-05-May/weathering_colored_pencils
Cheers,
Gene