2. Material Perspective: Reuse of Papyrus
A topic of study within the Crossing Boundaries project is the physical use and reuse of papyri in Deir el-Medina at the end of the New Kingdom.  One aspect of this study is to try and reconstruct the different stages in the life of a papyrus roll, sheet, or fragment. Egyptian papyri were often not only inscribed on one or both sides, but also wiped clean and used again, turning the manuscripts into palimpsests. In the case of the erased and usually illegible primary text of palimpsests, the relation between the direction of the script and the direction of fibres is often an important guide for understanding how the manuscript was used.  For this kind of research, close observation of material aspects of the object such as remaining ink smudges or fibre structure and direction are as important as the text written on the object.
An example of one such manuscript where material aspects reveal information about its history of use is P. Turin Cat. 2003 (Figure 2). The papyrus bears a text dated to the third year of Ramesses XI (22nd day of the first month of the Akhet season) in which a scribe called Thutmose takes account of certain commodities which appear to represent either the debt or the repayment of the debt of the water-carrier Pakharu (for information on the manuscript, text content, publications, and further reference, see http://papyri.museoegizio.it/o/98). The text is written parallel to the fibres on the side which—following convention—has been identified as the front or recto of the papyrus. The back or verso is blank except for one barely legible line of text—supposedly a docket  —which is written at a 90° angle in relation to the text on the recto thereby running parallel to the fibres as well. The general format of the manuscript—a rectangular shape with two sheet-joins running vertically to the text  —and the regular, vertical breaks in the manuscript seems to suggest that it was originally part of a larger papyrus that was kept rolled up (Eyre 2013:24). With a height of 21.5 cm and a width of 29.5 cm this papyrus conforms more or less with the standard measurements of a half size roll.  It is also possible that this part was cut from the roll to be used as an independent note, a hypothesis which might be argued for by pointing to the straight left and right edges of the papyrus which likely represent cuts rather than natural breaks. The presence of the apparently unrelated sign at the bottom right corner of the manuscript might suggest the opposite, however, indicating that the preserved papyrus is a fragment of a larger manuscript.
This leads to the hypothesis that the papyrus as we see it now had a different format in its earlier life. It is possible that the manuscript held the same shape as now but was turned by 90°, though this would mean that the document had a vertical rather than the usual horizontal layout. Such a layout would be rare, but it is not unparalleled (e.g. P. Turin Cat. 2090+2096; one has to take into consideration, however, that this document is also a palimpsest that was used for several different purposes). Considering the unusual nature of such a format, one is left with the impression that this layout may not have been the first choice of the scribe but was instead motivated by the format of the available papyrus sheet. One might then speculate that P. Turin Cat. 2003 may have been reused twice, and that the last preserved text represents the third step of use (Figure 4).
3. Technical Perspective: Fibre Detection
The investigations above show that the course of the fibres or the existence and positioning of sheet joins on a papyrus can be important sources of information for the analysis and subsequent interpretation of a document. But the size and spacing of individual fibres also contain valuable information, as they represent the only reasonably constant size within an image—unlike the size of handwriting, for example—if no additional indicators such as rulers are given. The fibres are therefore a material property that it would be very desirable to be able to automatically recognise and read from an image. Herein lies a bipartite challenge: on the one hand, the recording of the objects such that sufficient structural information is contained in the digital image, and on the other hand, the development and training of algorithmic models that can automatically detect the fibres (Figure 5).
Digital images of papyri are usually created under varying conditions, and differ according to the capturing technique (scans or photography) used, the equipment, the lighting settings (including values like intensity, colour temperature, and direction of light), and more. Naturally, this has an impact on the resulting colour values in the image and the visible material structure. We assume that minor changes to the intensity of the light and its colour temperature will not have a major impact on the fibre detection setting, while slight changes in colour tone may also occur across adjoining originals in the same lighting, depending on the state of preservation and the material conditions. Both these aspects have to be borne in mind as any algorithm used on original papyri has to account for such differences. Our primary focus, however, is the direction of the light and the resulting shadows as these allow us to infer the structure. In a first testing step, we provide a consistent lighting environment and thus exclude as many disturbances as possible from the structural features. The test images are taken using a wide range of settings, including exposure and aperture, angles of light, raking light, and transmitted light from the back. We also use different backgrounds with varying reflective properties. As papyrus is a semi-transparent material, bright backgrounds reflect more light back to the fibres while dark backgrounds absorb most of it. Preliminary tests with a scanner have shown that this reflective behaviour has some noticeable impact on the contrast and the visibility of the fibre structure in the image (Figure 6).
Another interesting problem that may not come to mind immediately when working on modern or well-preserved papyrus is induced by conservational techniques used in the past. Some of these methods interfere massively with the visual quality of the papyrus. Gauze, for example, is a net-like fabric made from silk that was applied to papyrus to provide it with additional stability. This textile usually covers the full extent of the object and thus interferes visually with the underlying natural fibres. Furthermore, these nets were often attached with a very reflective glue, which adds additional brightened regions to scans or photographs that are not determined by the papyrus itself and mask its structure. Other historic restoration methods and their remains may cause less interference, though the removal of conservation papers used to fix the fragments sometimes leads to lumps of paper fibres and glue being left behind on the papyrus surface (Figure 7). The removal of glue and backing paper might also be the reason why the ink seems to have moved on some papyri in modern times, as can be deduced from the considerable quantity of black pigments accumulating around the (modern) cracks of the manuscripts. All these and other occurrences add noise to the image which makes it a little more difficult to describe the surface structure.
Finally, a suitable machine learning approach must be chosen and trained on this new data. We currently envision a deep learning approach with an artificial neural network capable of semantic segmentation. Neural networks are one example of a machine learning method consisting of layered networks of so-called neurons interconnected with each other (Figure 8). Networks with many subsequent layers are called deep networks and are usually combined under the term deep learning. Some deep learning architectures have already been applied to papyrus material and show promising results, e.g. for the creation of facsimiles (Dhali et al. 2019) or the detection of text baselines (Grüning et al. 2019; Kiessling et al. 2019).