This report describes an ongoing project initiated in late 2012 to investigate the use of chain line pattern (CLiP) matching for the detection of mould mates (sheets made from the same papermaking mould) in the European paper used for printing Rembrandt’s etchings. We investigate the application of computer-based image processing tools to mark, measure, and compare the idiosyncratic intervals of chain lines as recorded in beta-radiographs of individual sheets in the hunt for mouldmates. Results indicate that CLiP has strong potential for investigating and matching papers used by Rembrandt and other early modern printmakers. It provides a new method that can identify related objects even in the absence of a watermark.