2.4.2 Uses of Spectral Imaging in Cultural Heritage
Multispectral and hyperspectral imaging have provided researchers in cultural heritage with the means to identify previously invisible elements of heritage objects and aid in monitoring, maintenance, and conservation processes. In this page, you will explore a few characteristic examples of spectral imaging, focusing not so much on the technical details but on the interpretative potential of the methods.
The first example is the World Map by Henricus Martellus drawn in 1491. Martellus was a German cartographer, and probably one of the most influential in the late 15th century. Evidence points out that Martellus' amps influenced among others, Christopher Columbus and Martin Behaim, who created the Erdapfel in 1490-92; the oldest surviving terrestrial globe. The map was donated to Yale University in 1962, however, despite its undeniable value, its condition of preservation has made it difficult to fully identify the text and other details. In 2014, a team of specialists under the direction of Chet Van Duzer (2018), applied multispectral imaging in order to see if they can identify details beyond those that are visible to the naked eye. The results indicated some of Martellus' sources and influences. For example, regarding his depiction of Africa, it was originally thought that Martellus used the Egyptus Novelo map, which survives in three manuscripts of Ptolemy’s Geography and was based on information shared by three Ethiopians (Council of Florence 1441). However, the multispectral imaging of the map demonstrated that that southern Africa extends to the east beyond what is depicted in Egyptus Novelo, therefore indicating that Martellus based his depiction on a more complete map. The imaging also provided indications of how Martellus' map influenced others created later, such as the world map by Waldseemüller (1507), which included many of the place names that originally appeared in Martellus' map. Other interesting texts indicate how the world was perceived at that time. For example, text in the southern Asia part of the map describes the 'Panotii' people as 'monsters similar to humans whose ears are so large that they can cover their whole body'. In northern Africa it talks about the 'large wildernesses in which there are lions, large leopards, and many other animals different from ours'. In central Asia, it describes the Hippopodes who 'have a human form but the feet of horses.' In the video below you can watch Chet Van Duzer talking in detail about the map and the results of the hyperspectral imaging.
Chet Van Duzer talks about Henricus Martellus's World Map at Yale. He describes the process of multispectral imaging and how the results have enabled him to situate the Martellus map in late 15th- and early 16th-century cartography.
One of Ötzi's tattoos identified by multispectral imaging (Samadelli et al. 2015). Click image to enlarge and see more images in the slideshow below.
Another interesting example is that of Ötzi, the Iceman. As mentioned in the previous lesson, Ötzi was found in 1991 in the Italian Alps. As his body was covered by snow it was well preserved, therefore allowing researchers to apply both conventional and digital methods to study the reason behind his death, his diet, and even his voice. A recent multispectral analysis of his skin (Samadelli et al. 2015) enabled researchers to determine the exact number and location of his tattoos. The tattoos on Ötzi's body were previously identified; they were produced by piercing the skin and then rubbing charcoal dust. However, because of the dark colour of his skin and because some of the tattoos have faded, it has been impossible so far to determine the location and exact number of all the tattoos. Previous studies have indicated up to 59 tattoos. Multispectral imaging for this study was conducted by using a modified DSLR camera, which allowed the capturing of wavelengths from 300nm to over 1000nm (from ultraviolet to infrared). This study identified the presence of 61 tattoos. The precise identification of tattoos in combinations with other analytic methods applied to the body, can prove useful in further analysis also related to the reasons for applying these tattoos.
Censored Postcard sent on April 9th 1942 from Egon Heysemann to Rolf Rotschild (Kleber et al. 2012). Click image to enlarge and see more images in the slideshow below.
The following example comes from the more recent history, the second World War. Kleber et al. (2012) applied multispectral imaging to a censored postcard send by Egon Heysemann on the 9th April 1942 from the Ghetto Piaski in Poland to his friend, Rolf Rotschild, who managed to escape to Sweden. Although the postcard reached the recipient the details of the trip and the situation in the ghetto were censored. In this case, and due to the heaviness of the black ink that was used by the censor, not much of the censored text was revealed. However, there is a clear potential here in using the method to identify text not previously legible.
The last example comes from the Neolithic past and an assemblage of clay figurines unearthed in Koutroulou Magoula in Greece. Multispectral Photography (Papadopoulos et al. 2019) was applied to a selection of figurines in order to identify and further enhance faded colour traces as the detection and visualization of pigment-based colour, enable not only new understandings of different technological processes but also provides information on decorative details that would have been otherwise missed, or not clearly understood. In this case as well, a modified DSLR camera (Nikon D700) along with special filters that isolate particular regions of the spectrum (daylight, infrared and ultraviolet) were used to photograph 16 figurines with degraded remains of painting. In the case of the sitting female figurine of the squatting type, multispectral imaging allowed us to detect and illustrate decorative patterns that were not visible, or not clearly visible on the 3D model produced through Structure from Motion (See Unit IV) which only captured visible light. While at the lower back of this figurine a pattern of red vertical bands is visible even with the naked eye, other decorative details, such as the belt, the vertical bands on the upper part of the body and the collar around the neck, were clearly detected and illustrated. The decorative details detected allow us to hypothesize that the intention of the crafts person here was perhaps to depict elements of a dress through these fine traces. An alternative scenario thus is that these painted features are not intended to denote elements of dress, but consist merely of bodily decoration destined perhaps to direct attention to specific anatomical features such as the neck, the wide back, the waistline, or the robust upper legs. Moreover, the use of red pigment to denote specific facets of identity such as gender, age, or status, cannot be excluded.
Slide Show: Examples of Spectral Imaging in Cultural Heritage
Quiz: Spectral Imaging in Cultural Heritage
References
Kleber, F., Hollaus, F., & Sablatnig, R. (2012). Multispectral Image Analysis of a Censored Postcard from 1942. InEarl et al. (eds) Archaeology in the Digital Era Volume II, CAA 2012, pp. 258-263. Amsterdam University Press.
Papadopoulos, C., Hamilakis, Y., Kyparissi-Apostolika, N., & Díaz-Guardamino, M. (2019). Digital Sensoriality: The Neolithic Figurines from Koutroulou Magoula, Greece. Cambridge Archaeological Journal,29(4), 625-652.https://doi.org/10.1017/S0959774319000271
Samadelli, M., Melis, M., Miccoli, M., Vigl, E. E., & Zink, A. R. (2015). Complete mapping of the tattoos of the 5300-year-old Tyrolean Iceman. Journal of Cultural Heritage, 16(5), 753 758. https://doi.org/10.1016/j.culher.2014.12.005
Van Duzer, C. (2018). Henricus Martellus’s World Map at Yale (c. 1491): Multispectral Imaging, Sources, and Influence. Springer.
Slide Show: Examples of Spectral Imaging in Cultural Heritage
Quiz: Spectral Imaging in Cultural Heritage
