Hello Dreadnought,

Sounds risky to me. I wouldn't want to wash my trains with cold cream.

However, you can try using dry pastels which you can find at a fine arts store or a "Micheal's" if you have one in Niagara. You should be able to buy individual colours of your choice there. Then grind them into a powder. This comes off with care, however I suggest its always best to test.

Alternatively you can try Pan Pastels which sell "weathering kits". I couldn't resist buying these at the Big E show in Springfield. Much more expensive though. George's Trains and Credit Valley....closer to you than me... carry them as indicated by a link on this website.
http://www.modelingcolors.com/
No doubt you can order them somewhere online too.
- Mark

ps. [Edit] Come to think of it, buying a few dry pastel sticks would be cheaper and more emotionally sane than swiping from your FDs make up kits.

Alex "the crazy russian" has a 30 minute demo weathering the pan pastels. Just to say, they are really good quality, very finely ground, but I would try a few dry pastels locally before ordering these. You can skip the first few minutes of Alex's intro where he talks about his new camera, but you'll get a good sense of how they work with this.