Determining the fibrillar orientation of bast fibres with polarized light microscopy: the modified Herzog test (red plate test) explained

Abstract

The identification of bast fibre samples, in particular, bast fibres used in textiles, is an important issue in archaeology, criminology and other scientific fields. One of the characteristic features of bast fibres is their fibrillar orientation, referred to as Z- or S twist (or alternatively right- and left-handed fibres). An empirical test for determining the fibrillar orientation using polarized light microscopy has been known in the community for many years. It is referred to as the modified Herzog test or red plate test. The test has the reputation for never producing false results, but also for occasionally not working. However, so far, no proper justification has been provided in the literature that the ‘no false results’ assumption is really correct and it has also not been clear up till now, why the method sometimes does not work. In this paper, we present an analytical model for the modified Herzog test, which explains why the test never gives a false result. We also provide an explanation for why the Herzog test sometimes does not work: According to our model, the Herzog test will not work if none of the three distinct layers in the secondary cell wall is significantly thicker than the others.

Great Potential of Stinging Nettle for Sustainable Textile and Fashion

“…Fibre is nettle. At α = 45° zero-order grey is clearly observed, which proves the expected positive sign of elongation[16] The modified Herzog test performed on (a) nettle (S-twist) and (b) jute (Z-twist). To the left the sample orientation angle α ≈ 0°, to the right the sample orientation angle α ≈ 90°[16] …”

“…Recent studies by Haugan and Holst [16] developed theoretical model for distinguishing natural fibres like jute, nettle, cotton, etc. and found that the fibril structure and their angle is different for all fibres based on polarised microscopic views and birefringence results.…”

Is It Hop? Identifying Hop Fibres in a European Historical Context

“…In recent years, there has been an increased interest in the scientific identification of archaeological and historical plant fibre material (see, e.g., Bergfjord et al . ; Haugan and Holst , ; Skoglund et al . ; Lukešová ; Lukešová et al .…”

Flax look‐alikes: Pitfalls of ancient plant fibre identification

“…Cotton, the most prominent textile plant in modern times, only became available in Europe at a much later date. Furthermore, cotton is not a bast fibre and can easily be distinguished from bast fibres using a polarization microscope (Luniak , Haugan and Holst ).…”

“…The modified Herzog test, originally developed by Herzog (Herzog ), is described in several places in the literature (Luniak ; Herzog ; Goodway ; Petraco and Kubik ). A detailed description together with the first analytical model of the method was recently presented by the authors of this paper (Haugan and Holst ). X‐ray micro‐diffraction can be used to identify ancient fibres.…”