A FOAF has some naptha that when evaporated leaves a thin film. As far as he can tell, the film is odorless and tasteless. In a dream, he completed a control evap on naptha that was unused in any other processes. He found the same result (film), albeit lighter and less noticeable. Is there some way to get rid of this? Is there any brand of naptha that anybody out there knows about that evaps completely cleanly? This person would like to perform a recrystallization, but is reluctant to with the same solvent. Can anybody give some advice as to how this person should proceed?