How does my Written Artefact change through time?

Diachrony

Stylianos Aspiotis, Olivier Bonnerot, Anna Schulz

Another field in artefact profiling concerns the effects that environment and human usage have on it. Many materials are prone to weathering which can alter their appearance, as well as their material profile. This is particularly detrimental in the case of written artefacts, as the changes can considerably alter the legibility of the objects. Even the most persistent writing surfaces in time, i.e. rock-based writing supports, will undergo changes due to weathering that reflect the prevailing environmental conditions and activities of anthropogenic origin. The influence of environmental conditions is so decisive that it determines the nature of the weathering products formed, as has already been shown in the case of inscribed marble supports in a Mediterranean and temperate urban oceanic climate. Several other examples include the formation of films of metal oxalates as degradation products on the surface of stoneware (Miliani et al., 2009), ancient monuments (Conti et al., 2012) and painted artefacts (Zoppi et al., 2010), as well as darkening processes of red-coloured paintings (Maguregui et al., 2014) and the growth of weathering-related products, in the form of crusts, on marble-made sanctuaries in an industrial environment (Moropoulou et al., 1998).

Of course, less durable writing surfaces can also be affected by weathering processes. For example parchment is prone to deterioration due to humidity and microorganisms. Such deterioration drastically changes the appearance of the parchment, making some areas purple or even leading to the detachment of some parts (Migliore et al. 2019). Even when paper is uncoloured, it can be susceptible to weathering due to the prevailing environmental conditions and biological activity. The combination of these deterioration-leading factors can have a visual effect on the paper, known as paper yellowing, but can also change the material composition of the paper. The latter has already been characterised by ATR-FTIR spectroscopy, which showed that the chemical ageing processes of paper are related to cellulose modification and lignin degradation reactions (Tinter et al., 2018). Considering that cellulose is an organic compound obtained from wood pulp, the ageing of wood in terms of molecular decay processes, is well documented (e.g. Inagaki et al., 2018) and has recently led to the development of a dating tool based on the molecular decay of wood (Tinter et al., 2020). 

The corrosive effect of some iron-gall inks on paper and parchment, leading in some cases to holes in manuscripts, is a well-documented phenomenon (Kanngießer et al. 2004). Similarly, some changes in pigment's appearance, like the blackening of white lead (Vagnini et al. 2018) are well-known phenomena, of which scholars and scientists should be aware when investigating coloured written artefacts.

In this regard investigations aim for example to search for key elements that can connect to specific environmental conditions in which the WAs have been kept and the ways in which usage has affected them. See also conservation and degradation.

As objects persist through time, they accumulate not only the effects of natural weathering and degradation but also frequently bear signs of reuse that result either from new writing initiatives or from palimpsesting, erasures, or censorship.

Examples: 

• certain fungi present on the surface of WAs have been for example linked to biodeterioration in parchment (Migliore et al., 2019) and can be studied by means of DNA analyses
• study of the weathering-related products and foreign particles found on/ beneath the WA’s surface to unravel lost or hardly readable inscribed text by means of non-destructive analytical methods such as Raman and FTIR spectroscopy and destructive ones including powder XRD and WD-EMPA (see also Can you read damaged or hidden writing from my WA?).