New insights with virtual archaeology
New insights with virtual archaeology
The state of Lower Saxony in Germany relies on industrial computed tomography for the research and restoration of cultural treasures
For museums and restoration workshops, the recovery and restoration of archaeological artifacts is usually a labor-intensive, time-consuming and costly undertaking. And on top of that: It is especially important not to damage the recovered items. Therefore, it is a decisive advantage to obtain non-destructive insights into the interior of finds before hands and mechanical tools are applied to uncover artifacts.
Only by looking inside it is possible to determine in advance how best to uncover or restore objects¬ and sometimes whether the find is indeed a spectacular one worthy of further research and restoration.
State-of-the-art digital non-destructive analysis methods, which are also used in industry for quality testing and in materials science research laboratories, are required to gain the most accurate insight possible into the inner workings of ancient finds, some of which are surrounded by soil or corrosion products, as in block excavation. With the help of modern industrial computed tomography (CT) archaeology can achieve what is also crucial in the examination of materials and components: making hidden things visible so that fine-mechanic tools and brushes can later be applied in the right place.
Recognizing object features in 3D
The industrial CT method is particularly suitable because it enables the creation of 3D volume data sets of complex objects that reveal details of just a few micrometers in virtual sections. Unlike classic X-ray images, the details are not superimposed by other structures. Another advantage is that it can be used to examine not only highly absorbent materials such as metals, but also materials such as residual fibers, ceramics or wood, which is essential for archaeological investigations.
Micro- and nano-CT in particular make it possible to sharply image even the smallest and sometimes crucial details. With the help of this method, a restorer knows exactly what is hidden beneath the surface of a find. By displaying it in 3D volume with a CT system, the respective artifact can also be documented as a kind of "digital twin" in its original state prior to further exposure and restoration measures. Likewise, questions about the state of preservation of a find or about existing corrosion can be answered precisely. This not only makes it easier to decide on the further conservation treatment of the find, but often also provides initial clues as to the chronological classification of the object.
Furthermore, micro CT scans allow for the detection and documentation of processing and use traces on the surface of archaeological objects, as far as the state of preservation permits - valuable information for archaeology.
One technology for numerous finds
State-of-the-art industrial CT technology from Waygate Technologies has also been used in numerous spectacular archaeological discoveries in Germany’s federal state Lower Saxony. As part of more than a decade of cooperation between Waygate Technologies and the state office for the preservation of historical monuments in Lower Saxony, Niedersächsisches Landesamt für Denkmalpflege (NLD), a wide variety of significant excavation pieces were scanned over several years in high-resolution CT systems of the Phoenix V|tome|x series at Waygate Technologies’ Customer Solutions Center in Wunstorf, and initial visualizations were created. The subsequent segmentation and analysis of the 3D volume data sets then took place at NLD in Hannover.
Preserving cultural treasures for posterity
But why go through the trouble of CT scanning and segmentation before moving on to manual precision work? In fact, there are numerous application scenarios that prove that CT plays a key role in modern archaeology. This is especially true for the preservation of ancient cultural artifacts, as the non-destructive method ensures that objects remain digitally intact. This method helps in dating objects, as well as in detecting certain particles and fibers such as textiles.
Virtual exposure through virtual slices
In 2016, an early medieval Sax sword found in Visbeck, Germany, and recovered within a block of surrounding soil, was examined using a Phoenix V|tome|x L 450 computed tomography scanner. The virtual sections through the scan volume of the 75 cm long sword, which had already been classically x-rayed in two dimensions, revealed two surprises shortly after scanning:
the scabbard of the sword was studded with rivets, which in turn were decorated with very small bead wire ornaments. Even the higher gray values compared to the iron suggested that these were silver rivets. This presumption was confirmed during the subsequent uncovering. A closer look at the handle also revealed another small knife on the right side under the sword.
Thanks to the CT, it was not only possible to document an exact 3D model of the sword and its grave goods, but during the subsequent uncovering it was clear from the outset where pure earth was to be expected and where special caution was required because important details were being approached.
The 3D information obtained by means of CT is therefore an invaluable advantage because it saves time on the one hand and helps to increase the quality of the restoration on the other.
Digital rust removal - Exposure at the click of a mouse
When metallic objects in the soil corrode, their X-ray absorption decreases due to the absorbed oxygen compared to the remaining pure, denser metal. This opens the possibility to hide the specific gray values of the corroded material around the remaining metal core and the adhering soil in the histogram of the CT volume data set simply by mouse click.
For example, a virtual post-processing of the CT volume dataset and the coloring of the individual objects made it possible to identify a conglomerate of 16 hammers and picks, presumably from the 16th century, found in Sankt Andreasberg in 2018.
Another example of this non-destructive method is a crusted Roman coin roll found in 2013 in Westerloh in the Hümmling. The coins were covered beyond recognition with a layer of corrosion of varying thickness. The separation and exposure of the coins required for dating in conjunction with wet chemical treatment, would have resulted in a significant loss of substance. A section through the stack revealed that there was a total of nine coins. However, after a micro-CT scan and its 3D reconstruction, it was possible to virtually leaf through the stack of coins layer by layer with comparatively little effort. In the process, symbols and portraits of rulers repeatedly became visible. These allowed a non-destructive classification of the find in the middle of the 4th century.
The results obtained, the successful dating of the individual coins and the use of the images ultimately justified the decision to leave the coin roll in the coherent find and thus preserve it for posterity.
Another example of virtual exposure is an iron belt buckle with silver overlays from an ancient Saxon burial ground that was scanned at Waygate Technologies, partially restored and heavily corroded. After the surrounding material was masked out in the CT volume, both the iron ring and the silver overlays could be made visible. It was also possible to visualize other decorations that remained undetected during the previous X-ray examination.
Digital lumber - virtual dendrochronology
While classical dendrochronology can rely on cross-sections or drill cores for dating historical buildings, for example, this method was not applicable to unique works of wood art or musical instruments for a long time due to their destructive nature.
In 2004, for example, a microfocus X-ray tube built by phoenix|x-ray (now Waygate Technologies) was used to scan three wooden Celtic cult figures in southern Germany i particularly high resolution. This made it possible to visualize not only medullary rays and annual rings, but even individual wood cells in a non-destructive virtual section. This not only proved that all three figures had been carved from the same oak, but also enabled the world's first virtual dendrochronological examination. This way the three cult figures could be dated exactly to the year 127 BC.
A high-tech glimpse into the Stone Age
The potential of high-resolution CT scanning has also been used to study prehistoric wooden tools. In the 1990s, several wooden spears and throwing sticks were discovered in the Schöningen open-cast lignite mine – the oldest completely preserved hunting weapons in the world. Dating back around 300,000 years, these wooden objects offer an unprecedented insight into the early ingenuity of the ancestors of Neanderthals (Homo heidelbergensis) during the Paleolithic period. They provide important information about the hunting practices and social organization of early humans. In recent years, the artifacts have been studied in an interdisciplinary research project led by the NLD (Lower Saxony State Office for Heritage).
The focus of the research was a double-pointed throwing stick, which was probably used to hunt small game and birds at distances of up to 30 meters. The results impressively demonstrate the skills of early humans: the stick was made from a carefully debarked spruce branch and shaped into an aerodynamic and ergonomic throwing tool. Traces indicate that early humans deliberately worked the wood to avoid cracks and warping. This suggests a surprisingly advanced understanding of the material's properties.
The micro-CT images, taken with a Phoenix V|tome|x M 300 scanner from Waygate Technologies, allowed the scientists to determine the internal structure of the wood. The 63 very closely spaced, eccentric annual rings visible in the CT scans prove that the extremely hard wood, resulting from very slow growth, was not taken from the trunk like the spears, but from a branch of an extremely slow-growing spruce – perhaps from the higher elevations of the low mountain ranges. This made it significantly harder than the spruce available in the region today.
After prolonged use, the throwing stick was probably lost near the lakeshore and quickly embedded in the mud. This rapid burial allowed preserved the artifact, but also left its mark: trampling damage, fungal infestation, root damage, and compression.
The analyses confirm the interpretation that the stick was used as a throwing stick and thus as a hunting weapon and underline the highly developed woodworking skills of early humans 300,000 years ago. The finds from Schöningen in Lower Saxony, Germany, are thus an impressive testimony to the ingenuity and adaptability of our human ancestors.
Neanderthal artistry unveiled
In another case, an early 'artwork' by Neanderthals was examined using a Phoenix V|tome|x M micro-CT scanner. The find was discovered in 2019 at the former entrance portal of the Unicorn Cave in the German Harz Mountains. The object is a foot bone of a giant deer, which Neanderthals had decorated with a geometric angular pattern more than 50,000 years ago. Based on the CT scans, a digital 3D model of the surface was created at the NLD. The task was to examine the processing traces of the engravings more closely in order to draw conclusions about their origin. It was found that the few millimeter-deep notches consisted of a vertical, partly stepped profile, followed by a horizontal plane. Archaeological experiments revealed that these patterns could be most effectively created through a combination of vertical incisions into the bone followed by scraping of the surrounding surface. The experiments also showed that these rather deep notches could not be produced in less than 90 minutes. The Neanderthal thus had enough time to ponder over this object and its meaning. The CT scan also allowed metric data to be collected on the 3D model, which interestingly highlighted the precision of the work. The individual notches have distances of 8-10 mm between each other and meet at an angle of about 90°. This unexpected precision was a surprising insight regarding Neanderthals.
Invaluable advantages through CT technology
After two-dimensional X-rays have been a standard aid in the restoration of archaeological artifacts for decades, industrial CT recently began documenting them in their original condition in high-resolution and three-dimensional images. It allows to accurately predict what to expect in a block excavation, an urn or in completely corroded conglomerates, whether restoration measures are worthwhile, and at the same time also predicts with millimeter precision at which points special care is required during uncovering.
In the case of valuable wooden objects, non-destructive tree-ring analyses become possible, and 3D printing can be used to create detailed exact copies not only of the surfaces accessible to laser scanners, but also of the interior.
Thanks to tremendous technological advances in recent years towards ever higher resolution results with ever shorter scan and reconstruction times, industrial CT has long since made the leap from research and quality labs to current production lines in the aerospace, automotive and electronics industries. Given its invaluable advantages, hopefully museums and restoration workshops will continue to be equipped with industrial CT technology in the future.