Welcome to the forums.
You need to add this gentlemen’s website to your list of favorites, you’ll be glad you did.
http://www.swannysmodels.com
And specifically
http://www.swannysmodels.com/Weathering.html
Disclaimer: I am not an affiliate of Swannysmodels.com and do not receive any compensation for answering every question by posting his web address…yet. Just kidding, but it is a helpful site. Besides my loyalty can’t be bought…rented yes, bought no!
My name is Dan the Model Grandpa and I approved this message.