Identifying plant fibres in cultural heritage with optical and electron microscopy: how to present results and avoid pitfalls

Identification of archaeological and historical textile fibres is important because it gives insight into resource management in former times. The arrival of new tools such as table-top scanning electron microscopes, have led to an increased interest in the topic. Unfortunately, there have been cases where a lack of documentation regarding instrument settings and selection criteria has led to questionable conclusions being drawn. Optical and scanning electron microscopy are powerful techniques, but they must be used correctly and with proper knowledge of their limitations. Furthermore, ancient fibre material is often difficult to examine due to issues such as sample degradation, mineralization and the scarcity of material, which means that conclusions based on a statistical analysis of a large number of fibres are essentially not possible. In a cultural heritage context, it is therefore essential to distinguish between characteristic features, by which we mean features that are often, but not always present in a particular species and distinguishing features, which are always present in a particular species and can therefore be used for identification even if only a small amount of sample material can be examined. We argue that the community will have to accept that, quite often, a secure identification is not possible and that absolute statements such as: “This textile is made of flax” will often have to be replaced by relative statements such as “The material is likely to be flax”. In this paper, we address these issues as follows: first, we present a fibre identification diagram which can be used, with some limitations, to distinguish between flax, hemp, nettle, jute, hops, and cotton using optical and electron microscopy. We then move on to highlight some of the typical pitfalls of using optical and electron microscopy for fibre identification. Finally, we present measurement documentation tables for optical and electron microscopy images, which we suggest should always be included in publications. Material scarcity means that the amount of material used for investigations should be kept at an absolute minimum. It is thus crucial that results are published with proper documentation so that measurements do not need to be repeated (more material is used) in future studies. It is our hope that the measurement documentation tables will be adapted by the community and used in future publications in the field. The paper finishes with a demonstration example, presenting a fibre analysis of Viking Age textile fragments from the 10th Century with documentation tables.