Tapestries and especially pile carpets can be challenging objects for assessing their photosensitivity by microfading: they are often made of relatively thick yarns resulting in a non-flat airy surface. For this reason, focusing the light on the object’s surface is difficult and the precision of the colour change measurement is hampered. In this study, an improved test methodology was developed to overcome the difficulties by analysing single yarns. The methodology consists in flattening the yarn between glass microscope slides tightly held together by means of 4 strong paired neodymium magnets. The results show that the newly-developed sample preparation together with the required instrumental adjustment allow to significantly reduce the standard deviation and variation coefficient which often characterize microfading measurements of textiles. The methodology for sample preparation is evaluated and had been applied to samples from the Reformation Tapestry dating to 1667 from the collection of the Museum Europäischer Kulturen (Museum of European Cultures) in Berlin.