How to date my Written Artefact?
Stylianos Aspiotis, Olivier Bonnerot, Sebastian Bosch
Unfortunately, non-destructive analysis cannot deliver an absolute age of written artefacts. The well-established method of dating by radiocarbon results in a range of absolute ages for organic surfaces such as papyrus, parchment, or textiles (Hajdas et al. 2021). Radiocarbon dating, or 14C dating, was developed in the middle 1940s (Libby 1946) and is based on the following principle. 14C is a radioactive isotope (member of an element with the same number of protons and different number of neutrons in its nucleus) of carbon that is naturally produced in the atmosphere by the interaction of cosmic rays with atmospheric nitrogen. 14C is then combined with oxygen, to form radioactive CO2, which can be incorporated into plant tissues through photosynthesis and into animals through the well-known food chain throughout their lives. After the death of the living organism, the 14C content undergoes radioactive decay, i.e. starts to decline with a half-life of 5,700 ± 30 years. Thus, by measuring the amount of the remaining 14C content, a direct correlation to the absolute age of death of the living organism can be established. However, the oldest dates that can be reliably measured should not exceed 55,000 years ago (due to the short half-life). Moreover, very precise sampling is required due to the dangers of organic contamination, preservation techniques, and conservation conditions (e.g. Margariti et al. 2022), but the amount needed is limited to less than 1 mg.
Other techniques for absolute dating include dendrochronology and thermoluminescence. Dendrochronology is based on the principle that trees produce annual growth rings that vary in width depending on the environmental conditions of each year. A reference chronological sequence of tree rings can be reconstituted for several centuries by measuring and comparing the width rings in living trees and securely wooden objects for each region of interest. This sequence can be used to date wooden objects or structures by matching their tree rings with the reference sequence of the region. Thermoluminescence is based on the principle that some minerals and crystalline materials emit light when they are heated, after being exposed to ionising radiation. The radiation causes electrons to be trapped in defects or imperfections in the crystal lattice of the material. When the material is heated, the trapped electrons are released and recombine with holes, emitting photons in the process. The amount of light emitted is proportional to the accumulated dose of radiation received by the material. Thermoluminescence can be used to date objects that contain such materials, such as pottery, ceramics, and volcanic rocks, by measuring the intensity of the light emitted and calculating the time elapsed since the last heating of the object. However, all these methods require sampling of the objects and are therefore often not possible.
Indirect or relative dating methods, on the other hand, do not provide information about the absolute age of a written artefact, but rather about its relative age. This means that no information about the year of production or the timing of specific events in the timeline can be derived, but rather the chronological order of these events, since relative dating methods are based on the principle of stratigraphy (for more information, see Artioli 2010).
Recently, spectroscopic methods that can be used on site and non-invasively have been applied for age estimations of written artefacts and can therefore be considered as relative dating methods as well (Nesměrák and Němcová 2012). XRF spectroscopy has proven to be a promising method for determining the elemental composition of iron-gall inks and inorganic colourants. The identification of these materials and its impurities can finally provide information on the chronological classification of an object. Hahn et al. (2005) showed that XRF spectroscopy together with a semi-quantitative evaluation method (fingerprint model) is capable of classifying different iron-gall ink types, which in some cases can be dated due to their impurities. In one fragment the researchers identified chromium as an impurity in one ink. The presence of chromium indicates that it was not applied before the beginning of the nineteenth century, when the use of substances containing chromium (e.g. as pigment) was proposed for the first time (after L. N. Vauquelin had discovered the element chrome in the mineral crocoite in 1797). This allows for an indirect dating of this ink with a terminus post quem. Similarly, the identification of modern or synthetic pigments can provide information about the temporal production process of an object. Bosch and Janke (2021) could prove that the coloured decoration of a mediaeval antiphonary was only added in the 19th century, since they identified modern pigments, such as zinc white, certainly unknown in the Middle Ages (see Case Study "Indirect Dating of Italian Manuscripts Copied from the Squarcialupi Codex".
Other destructive approaches, such as measuring the shrinkage temperature of parchment (Burton et al. 1959) and identifying fibres and fillers through paper analysis can also be used to determine its date and origin.
Another possibility for dating manuscripts made of paper is the study of watermarks. Starting from the late 13th century CE, some papermakers were modifying their mould by drawing marks with metallic wires. These marks get transferred to the paper by locally reducing its thickness, and can be observed with transmissive light when the paper is dry. As watermarks are characteristic of specific makers, and were used only for a limited time, they can be used to give a post quem date to manuscripts, provided that they appear in one of the watermarks databases.