A few days ago I was reading through some art books I had check out of the library. There was one pastel book in particular that gave me a tip I have to share.Most people who own a set of soft pastels know how dingy they become. There was a particular set I own that were covered in so much mud colored pastel dust that I couldn't tell which color was which. I took the advice in the book and filled a container with uncooked rice. Then I put the pastels in, and shook it up. Almost immediately the pastels absorbed the excess pastel dust.
End result: Purple gray tinged rice and clean pastels!