Mysterious white spots on deteriorated brown papers can be seen in Dutch atlases produced during the 16th and 17th centuries. Why do these white spots resist the oxidation activity? Is there something in these white spots which stops further deterioration? On some examples the deterioration has proceeded so far that conservation intervention is required. But before that, it is essential to know more about the causes of the deterioration so that correct treatment may be given. Before beginning to analyze these maps, I have tried to gather information on historical and technological aspects of Dutch Map production.