Paper analysis in terms of the study of watermarks has generally concentrated on printed books and manuscripts. During the last 15 years however there has been a tendency to document watermarks from drawings in catalogues but their inaccurate rendering and superficial classification according to published sources, make them of little real value. A technique of watermark reproduction is described and practical problems are discussed. The example is given of the reconstruction of jacopo bellini's drawing book which was dismantled without recording the collaction. Watermarks positions and leaf format can thus be used to suggest probable original constructions. Diagram, 10 references notes.