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Mexicolore contributors Jerry Offner and Antonio Cosentino

Hi-tech imaging of two Aztec codices in Paris

We are sincerely grateful to Dr. Jerry Offner, Associate Curator of Northern Mesoamerica, Houston Museum of Natural Science and to Antonio Cosentino, Director, Cultural Heritage Science Open Source (CHSOS) for this exciting - if very technical! - report on their pioneering work in imaging two important Mexica (Aztec) manuscripts held at the Bibliothèque National de France, Paris.

Pic 1: Codex Xolotl, X.020, the ‘tlacamecayotl’
Pic 1: Codex Xolotl, X.020, the ‘tlacamecayotl’ (Click on image to enlarge)

Imaging the Codex Xolotl and Mapa Quinatzin at the Bibliothèque National de France, Paris, 14-15 June, 2016
On June 14 and 15, Dr. Antonino Cosentino of Cultural Heritage Science Open Source and I were able to carry out technical photography of the Codex Xolotl (pic 1) and Mapa Quinatzin (pic 2) at the Bibliothèque Nationale de France, Paris (BnF). Permissions, facilities and staff time were arranged by Laurent Héricher, Chef du service des manuscrits orientaux, Département des Manuscrits of the BnF. This was no easy task and we express our appreciation for the extensive effort and work he put into these arrangements, particularly in the midst of a multiyear renovation of the site Richelieu, where the documents are kept. Loïc Vauzelle, a graduate student at the Sorbonne, travelled from central France at his own expense to assist, and John Hessler, the Kislak Curator of the Library of Congress also happened to be in Paris and provided expert aid and observations as the process went on.

Pic 2: Mapa Quinatzin, leaf 3
Pic 2: Mapa Quinatzin, leaf 3 (Click on image to enlarge)

In addition, Dr. Marisa Álvarez Icaza Longoria of UNAM, who was at the BnF traveling on a fellowship, contributed valuable ideas. She had just participated in the Oxford conference “Mesoamerican manuscripts: new scientific approaches and Interpretations,” held 31 May to 2 June, 2016 which included several talks on imaging indigenous Mesoamerican documents [link below].
We were provided with a meeting room with two windows that we were able to cover with two layers of black plastic bags secured by green painter’s tape. For others who may be faced with a similar situation, it is worth noting that not one but two layers of these already two sided bags were needed to block the summer light sufficiently. Also, the BnF was happy to see that the painter’s tape left no marks on their walls upon removal. The meeting room door turned out to be light proof around its edges and needed no special attention. The room had only a standard meeting table, the height of which unfortunately could not be adjusted (pic 3).

Pic 3: Dr. Cosentino focusing in on Codex Xolotl X.050 and .060
Pic 3: Dr. Cosentino focusing in on Codex Xolotl X.050 and .060 (Click on image to enlarge)

We were able to capture four types of technical images for these Aztec pictorial documents. Antonino Cosentino used a modified full spectrum Nikon D800 digital camera, sensitive to the spectral range 360-1100 nm, along with different lighting sources and filters to obtain images that we can designate in this way:-
VIS (visible)
IR (infrared)
UVF (ultraviolet fluorescence)
UVR (reflected ultraviolet)
Because of the table height, we had to shoot at an angle, but Antonino made the best of this by making the IR images do double duty also as RAK images.

Technical photography documentation of the manuscripts

Pic 4: Preparing to acquire images from Codex Xolotl X.020
Pic 4: Preparing to acquire images from Codex Xolotl X.020 (Click on image to enlarge)

What do these designations for types of photography mean, and how are the images described by them acquired? VIS is used here for light in the visible spectrum, or the portion of the electromagnetic spectrum that is visible to the human eye. A typical human eye will respond to wavelengths from about 390 to 700 nm. In the procedure used for the documents, light, provided by fluorescent tubes, reflected off the surface of the document and passed through an X-Nite CC 1 filter which blocked infrared wavelengths before entering the lens and camera. The filtered light was then captured by the 36 megapixel CMOS sensor in the Nikon camera.
IR is the designation used here for infrared photography. In this case, a Heliopan RG 1000 filter was placed over the camera lens to block visible light while allowing infrared radiation into the camera. (Remember here that infrared radiation has longer wavelengths than visible light, while ultraviolet radiation has shorter wavelengths). As mentioned, these IR images also served as RAK images, meaning that the document pages were illuminated by an infrared source at an oblique angle. Although the angle we used was only slight, the images captured provide a great deal of information on the surface topography and relief of document pages.

Pic 5: Technical-Photography-Equipment-Filters-set
Pic 5: Technical-Photography-Equipment-Filters-set (Click on image to enlarge)

UVF imaging picks up visible light emission excited by a UV source (UV-LED) that is used to illuminate the document. As the surface is illuminated, certain materials fluoresce - that is, the material absorbs some of the UV radiation that falls on it and emits visible light. The photons which are then emitted from the document have longer wavelengths that fall into the normal visible light spectrum. Not all materials fluoresce so this method can be a valuable tool for distinguishing materials, and for seeing certain materials more clearly, such as European iron-gall ink glosses (see below). For UVF, two filters are placed in front of the camera - the X-Nite CC 1 filter mentioned above, and a Baader UV/IR filter. These filters work together to create a spectrum window that allows just the visible wavelengths produced by the UV-induced fluorescence into the camera, while blocking wavelengths of light outside the visible spectrum (pic 5).

UVR (reflected UV) imaging is simpler. The document is illuminated with UV light and the camera records the reflected light through another spectrum window created by the X-Nite CC 1 filter and a B+W 403 filter which allows UV waves into the camera. UVR photography is also another helpful tool for assessing surface topography and roughness.

Pic 6: Ice rafts on Europa, from the Galileo spacecraft on February 20, 1997, from a distance of 5,340 kilometers; Mapa Quinatzin, leaf 2, upper margin
Pic 6: Ice rafts on Europa, from the Galileo spacecraft on February 20, 1997, from a distance of 5,340 kilometers; Mapa Quinatzin, leaf 2, upper margin (Click on image to enlarge)

The images are taken sequentially without moving the document and can therefore be assembled into spectral cubes in Photoshop through the use of layers. Using features of this program, and harnessing the human eye’s exquisite sensitivity to detecting change, the various layers can be compared using a method not unlike the blink comparator that was used by Clyde Tombaugh to discover the dwarf planet Pluto in 1930.

The filter set used for the examination of the manuscripts
Understanding how the images are acquired helps us understand what we are seeing but also helps us develop methods to uncover or clarify details in these nearly five hundred year old manuscripts. Examining the surface of the images is also not unlike examining the images sent back by NASA planetary probes. In picture 6 the ice rafts on Jupiter’s moon Europa are seen side by side with rafts of “plaster” (gypsum, chalk, we still need to characterize this material) from the surface of the Mapa Quinatzin. Many, but not all, Aztec manuscripts were painted after a layer of “plaster” had been applied on top of indigenous amatl (amate) paper.

Pic 7: VIS, IR, YVF and UVR images compared
Pic 7: VIS, IR, YVF and UVR images compared (Click on image to enlarge)

We need to examine our images as carefully as NASA, JPL, and ASU examine their images, bearing in mind that it is considerably easier to acquire new images of the Mapa Quinatzin than of Europa.
In our case, let’s compare the VIS image with the IR, UVF and UVR images.
In this example, the damaged plaster fragments are seen well in VIS and UVR, while the IR image more accurately depicts the folding and flexing of the supporting indigenous amatl paper, and the UVR images shows mostly disturbance in the underlying amatl paper (pic 7).
Every landscape we encounter in the two documents that we imaged has the potential to teach us something new.
For example, a detail from Mapa Quinatzin, leaf 3 helps us read the alphabetic gloss in European ink better than it has been read for centuries (pic 8).

Pic 8: A small part of Mapa Quinatzin, leaf 3, is improved and rendered legible by the fluorescing of the support (the amatl paper) in contrast to the dark European iron-gall ink in the gloss
Pic 8: A small part of Mapa Quinatzin, leaf 3, is improved and rendered legible by the fluorescing of the support (the amatl paper) in contrast to the dark European iron-gall ink in the gloss (Click on image to enlarge)

Indigenous ink, composed of carbon black, is far more durable and less damaging to indigenous documents. The often corrosive European iron-gall ink happens to absorb UV radiation and so UVF can be a useful tool for reading alphabetic glosses on these documents because of the contrast with the support (amatl paper) that is generally brighter (because it fluoresces). This section of the manuscript was unfortunately trimmed during its long history and the meaning of this particular scene, showing a man conversing with someone in a building, along with a man punished by strangling, has remained obscure.
Mapa Quinatzin leaf 3 records a few Aztec legal rules along with cases of judicial corruption and their punishment. It is not just a list of rules but instead a fragmentary statement of precontact Aztec Texcocan jurisprudential thought, most likely presented, in this case, for European inspection. Such jurisprudential thought continued well after contact, and involved such issues as how Aztec legal process should be conducted and how certain cases with certain details should be decided and punished. Aztec jurisprudence was the product of sophisticated schools of thought over many years.

Pic 9: The oval room of the Bibliothèque National de France, Paris (Richelieu building)
Pic 9: The oval room of the Bibliothèque National de France, Paris (Richelieu building) (Click on image to enlarge)

In this set of images of a small part of Mapa Quinatzin, leaf 3, the UVF image is improved and rendered legible by the fluorescing of the support (the amatl paper) in contrast to the dark European iron-gall ink in the gloss. The Nahuatl text in alphabetic form that is revealed, of course, explains only a tiny portion of the meaning of the images: the indigenous Nahuatl graphic communication system was capable of communicating far more than mere alphabetic text could in a given amount of space. Nevertheless, what little the alphabetic gloss says helps us correlate the image with other lengthier dependent alphabetic texts, especially those of the expert early ethnographer and historian Ixtlilxochitl (1975), and yields enough information to change our understanding of the structuring of the indigenous content of Mapa Quinatzin leaf 3 and of Aztec jurisprudence as a whole.
The landscape provided by the new images is not as large as Jupiter’s moon Europa, but it is a significant undiscovered country that will provide many more surprises as it is examined. What was unknown proves again to be only temporarily hidden, and more things that remain unknown will hopefully be revealed through these images or through carefully designed new images and imaging techniques.

Picture sources:-
• All pictures by and courtesy of Jerry Offner, with the exception of -
• Pic 6 (left): image from NASA/JPL/ASU (public domain)
• Pic 9: photo by Poulpy, Wikimedia Commons.

This article was uploaded to the Mexicolore website on Aug 30th 2016

Conference on Mesoamerican Manuscripts 2016

Cultural Heritage Science Open Source, CHSOS

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