Cleaning the woofer JBL 4312 after hanging in a smoking studio.

hello :) my name is jeroen and i am the proud owner of a pair of jbl 4312. there is only one problem and that is that the woofers are not beige or white, they are totall brown from the nicotine. :(, i don not know if there is a coating on the conus or if it is just paper. does any one know , and more important what would be a safe way to clean it ? , hope someone knows :) kind regards Jeroen  :)