Tomografia a raggi X per manoscritti
10.6092/issn.2532-8816/14399
In questa review verranno presentati gli studi e i risultati ottenuti nell’ambito del progetto “Virtual X-ray Reading” dedicato alla tomografia X.&nbsp;
Il progetto VRX, partito nel 2014 presso l’École Polytechnique Fédérale de Lausanne (EPFL, Svizzera), era parte dell’ambizioso progetto “Venice Time Machine”. Il progetto VXR aveva lo scopo di testar la fattibilità e di sviluppare una tecnica di digitalizzazione di manoscritti alternativa basandosi sulla tomografia a raggi X. La ricerca e la tecnologia hanno fatto notevoli progressi nell’incremento della velocità di digitalizzazione e nella sicurezza dei processi di digitalizzazione di antiche collezioni ma, nonostante ciò, l’acquisizione di documenti antichi, fragili o mai aperti rimane una sfida formidabile. Grazie all’alto potere di penetrazione dei raggi X, con la tomografia è possibile l’acquisizione tridimensionale del volume dell’oggetto senza la necessità di aprire il documento. Il contrasto radiografico necessario per la leggibilità del documento è dato dalla composizione degli inchiostri antichi, come l’alto assorbimento X degli inchiostri ferro-gallici diffusamente utilizzati in Europa per secoli. In questa review presento gli studi condotti per sviluppare questa tecnologia, dalle indagini sulla chimica degli inchiostri, ai test di fattibilità condotti usando grandi facilities come i sincrotroni, dall’acquisizione di un libro manoscritto di 200 pagine, ed alla tomografia di un testamento veneziano del 14th secolo ancora sigillato.
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Ink Chemistry
X-ray tomography for manuscripts
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2022-06-22
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Um. Dig.
Fauzia Albertin
2022/06/22
10.6092/issn.2532-8816/14399
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Institute of Chemical Sciences and Technologies Giulio Natta SCITEC - Perugia
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Ink Chemistry
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X-ray tomography for manuscripts
https://umanisticadigitale.unibo.it/article/view/14399/14068
        Umanistica Digitale – ISSN: 2532-8816 – n. 12, 2022
F. Albertin – X-ray tomography for manuscripts
DOI: http://doi.org/10.6092/issn.2532-8816/14399



                     X-ray tomography for manuscripts

                                           Fauzia Albertin

        Istituto di Scienze e Tecnologie Chimiche “Giulio Natta” SCITEC, CNR, Perugia, Italy
                                  fauzia.albertin@gmail.com




       Abstract

This review presents the studies and the results achieved in the framework of the “Virtual X-ray
Reading – VXR” project devoted to X-ray tomography for manuscripts digitization. The project
started in 2014 at École Polytechnique Fédérale de Lausanne (EPFL, Switzerland) and was part
of the ambitious “Venice Time Machine” project. VXR aimed to test the feasibility and to
develop an alternate digitization technique for ancient manuscripts based on X-ray tomography.
Research and technology made considerable progress in increasing the speed and the safety of
the traditional digitization process of ancient collections, but, despite this, imaging of ancient,
fragile, or un-opened documents remains a formidable challenge. Thanks to the high penetration
of X-rays, the acquisition of a 3D – tomographic – volume is possible even without opening the
document. The X-ray contrast necessary for the readability of the text is strictly connected to the
chemical composition of the ancient inks, such as the high X-ray absorption of the iron gall inks
used for centuries in Europe. This review will present the studies conducted to develop this
technology, from the investigations on the chemistry of ancient inks to the imaging feasibility
tests performed using centralized facilities such as synchrotrons light sources, from the
tomographic imaging of a 200-pages manuscript book to the analysis of a 14th Venetian sealed
last wills.

In questa review verranno presentati gli studi e i risultati ottenuti nell’ambito del progetto
“Virtual X-ray Reading - VXR” dedicato alla digitalizzazione di manoscritti con la tomografia a
raggi X. Il progetto VRX è partito nel 2014 presso l’École Polytechnique Fédérale de Lausanne
(EPFL, Svizzera) ed era parte dell’ambizioso progetto “Venice Time Machine”. Il progetto VXR
aveva lo scopo di testare la fattibilità e di sviluppare una tecnica di digitalizzazione di manoscritti
alternativa basata sulla tomografia a raggi X. La ricerca e la tecnologia hanno fatto notevoli
progressi nell’incremento della velocità e della sicurezza dei processi di digitalizzazione di antiche
collezioni ma, nonostante ciò, la digitalizzazione di documenti antichi, fragili o mai aperti rimane
una sfida formidabile. Grazie all’alto potere di penetrazione dei raggi X, è possibile l’acquisizione
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del volume 3D – tomografico – dell’oggetto senza la necessità di aprire il documento. Il contrasto
radiografico necessario per la leggibilità del testo è strettamente legato alla composizione degli
inchiostri antichi, come l’alto assorbimento X degli inchiostri ferro-gallici utilizzati in Europa
per secoli. In questa review verranno presentati gli studi condotti per sviluppare questa
tecnologia, dalle indagini sulla chimica degli inchiostri antichi ai test di fattibilità condotti
usando grandi facilities come i sincrotroni, dall’imaging tomografico di un libro manoscritto di
200 pagine all’analisi di un testamento veneziano del 14th secolo ancora sigillato.



       Introduction

The project started in 2014 in the frame of the Venice Time Machine (VTM) project [1] and
involved the École Polytechnique Fédérale de Lausanne, the University Ca’ Foscari of Venice,
and the Archivio di Stato in Venice. The VTM project targeted the unlocking and transformation
in a digital data repository of the Archivio di Stato – 80 km of administrative documents. The
Archivio spans over ten centuries and documents every aspect of Venetian history, but the sheer
mass of data is one of the significant obstacles to its digitization. VTM aimed to study and figure
out new digitization approaches to speed up the process, transcribe and index a considerable mass
of manuscripts and make them available for historians and general public.

The use of X-ray tomography could facilitate and accelerate the first step of the digitization
process: without opening the manuscripts, throughout the 3D X-ray imaging, the entire
manuscript’s volume could be acquired and the information virtually extracted, page-by-page,
from the 3D tomography volume (Figure 1). This approach could make the “reading” of
manuscripts possible without opening them in a completely non-invasive way: the technique
strongly reduced the objects’ manipulation and eliminated the needing for page-turning,
drastically reducing the risk of damages.

To explore this new approach, I carried out numerous tests and analyses, from the chemical
investigation of the inks to the imaging with synchrotron source and conventional X-ray lab-
based imaging systems. Here, I present the milestones achieved, from the first chemical
investigation on a parchment fragment performed in 2014 to the tomographic imaging of a
sealed 14th century Venetian last will acquired with one of the transportable X-ray set-up of the
X-ray tomography for Cultural Heritage Laboratory of the Department of Physics and Astronomy
“Augusto Righi” of the University of Bologna.

The approach of VXR is based on pioneering projects that exploited X-rays to decipher
documents such as the use of synchrotron light to retrieve “lost” text from the “Archimedes
Palimpsest” with X-ray fluorescence [2]. V. Mocella pioneered the use of X-ray tomography to

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analyze handwriting in revealing letters in rolled Herculaneum papyri by X-ray phase-contrast
imaging [3], and the works of W. Seales et al. [4] [5] [6] and of G. R. Davis [7] posed solid bases
for the development of the tomographic technique for manuscripts. Furthermore, Patten et al.
[8] studied the potential document’s radiation damage.

Besides the studies I conducted in the framework of the Virtual X-ray reading project, and here
presented [9], [10], [11], [12], [13], [14], [15], recently impressive result was obtained using X-
ray tomography to virtually unroll a scroll from En-Gedi [16].

The success of these projects demonstrated the great potential of X-ray techniques in the study,
deciphering, and reading of ancient manuscripts. Moreover, these studies open the way to using
X-ray tomography to decipher texts on more variegated supports, such as the work by D. Stromer
et al. [17] and their research to the reading of a bamboo scroll [StromerBamboo2019] or the
scan of a film footages by Liu et al. [19].




               Figure 1: Traditional digitization vs. X-ray tomography digitization


Along the path to reading manuscripts using X-ray tomography, a critical issue is the nature of
the ancient inks. Before the advent of modern inks, two main groups of black inks were used for
centuries: iron-based ones and, less common in Europe, carbon-based ones. X-ray absorption
imaging is made possible for the first group by the heavy element content of the inks generically
denominated iron gall - that corresponds to a wide variety of ingredients and recipes [20]. On
the contrary, X-ray absorption contrast is weak for carbon-based inks - although imaging could
still be possible with alternate X-ray contrast mechanisms or with other imaging techniques.

Even if the use of iron-gall inks for centuries in Europe has been tested extensively [20], [21],
[22], [23], [24], recipes and composition of the inks used for “every day” documents (as opposed
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to pieces of high artistic or historical value) and for archival documents - such as notary papers,
work contracts, commercial transactions, and demographic accounts – is scarcely documented.
Furthermore, Archives such as the Venetian Archivio di Stato collection span ten centuries, with
inevitable fluctuations in the ink’s recipes.

The major challenge of using X-ray tomography for digitization was – and still is – the virtual
extraction of the manuscripts’ pages. The result of X-ray tomography is a 3D volume where each
pixel in the 3D volume represents the X-ray absorption of the point of the real object. The
identification, isolation, and extraction of the pixels related to the specific page are needed to
extract the document’s foils. Several approaches have been used, most of them dedicated to
papyrus tomographic imaging and their segmentation [25] [26] [27] [17] [28]. In principle, a
manual, supervised procedures or full unsupervised ad hoc algorithms are used to recognize and
classify pages, numbering them and recognize the empty space between them. Then, only the
classified pages will be extracted and rectified to be visualized. For these processes, the thickness
of the pages, the spacing between them, and the resolution and quality of the tomographic image
are crucial for a successful result. Unfortunately, the large variety of manuscripts – in forms, page
number, and materials – make developing a generic and highly flexible algorithm a hard goal.

The VXR project analyzed all these aspects of the X-ray tomography digitization, from the
chemical investigation of inks of “every day” documents to the feasibility study - with large
facilities and laboratory instrumentations - of X-ray tomography to read and to digitize archival
records and documents.



       Ancient manuscripts’ materials

The X-ray visibility of writings in X-ray tomography – named the X-ray contrast – is induced by
the difference in X-ray absorption between the support – the pages – and the writings.

Therefore, the chemistry of the inks plays a primary role: inks with a high content of heavy
elements, such as iron and metals, are visible in X-ray images. Contraries’, inks with a low content
of heavy elements or mainly composed of light elements, are almost invisible. Beside this, the
supports and their thickness play an important part in the feasibility of the technique. In Figure
2 a schematization of the main manuscripts’ materials and their visibility in X-ray imaging is
reported.

As mentioned, inks for writing could be divided into two main categories: black inks and colored
ones. For many centuries, in Europe, the most widely used black ink for manuscripts was the
iron gall, a name suggesting the presence of iron. Black inks with no heavy elements were less
common, such as the Roman atramentum scriptorium, based on lampblack with a gum binder.
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Although the generic iron gall formula corresponded to a wide variety of ingredients [20], the
basic fabrication process was an acid reaction with an iron compound. The most common
procedure involved tannic acid (C76H52O46) and iron sulfate (FeSO4) in rainwater, white wine,
or vinegar [29]. Tannic acid was obtained from plants, the richest source being the ‘galls’
produced by trees in response to parasite attacks (e.g. by gall wasps); for example, the British oak
galls or the top-quality Aleppo galls. Iron sulfate was known as ‘green vitriol’, extracted from
mines, notably coal mines. The reaction of tannic acid with FeSO4 produced, with oxygen
exposure, ferrotannate, a black pigment. In addition to the pigment, the black inks also contained
a water-soluble binder. One of the most common was gum arabic. This is a natural product of
trees, e.g. acacia, rich in polysaccharides and glycoproteins and its main component is arabin
[29], [30]. Other ingredients could be present, such as logwood pigment. A dangerous property
of iron gall inks is their corrosivity and their chemical attack to the substrate. The ink–substrate
interaction was extensively analyzed by [31], [32], [33] and [34] using techniques such as
synchrotron radiation XANES (X-ray absorption near-edge structure) and micro-fluorescence
techniques.

In addition to black inks, for important writings or illuminated manuscripts, colored inks were
used. Contrary to iron-gall inks, these inks are very similar to artist pigments. For them, the
scientific literature is much vaster [35] and the recipes remained unchanged for centuries, handed
down from one generation into another, from one bottega to other. These aspects make these
inks identification and study easier than for the black ones. Moreover, most of these pigments
are mineral and contain elements visible in X-ray [36], making techniques such as MA-XRF the
perfect approach to analyze them [37], [38], [39] and X-ray tomography feasible in most cases.

As mentioned, supports are important for the visibility of the writings. Even if the X-ray
absorption of almost all supports is similar and limited – cellulose or rag paper, parchment, wood
– a higher manuscripts’ thickness decreased the total X-ray contrast of the writings. For this
reason, almost all the supports could be digitized with X-ray tomography but a successful result
is strictly connected with the manuscripts’ thickness.




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        Figure 2: Main manuscript materials and their visibility in X-ray imaging

A revolution in the world of texts in Europe appended with the invention the “industrial”
printing by Johannes Gutenberg in 1455 [40], [41]. The production of books became extremely
rapid, exceptionally abundant in numbers, and increasingly less expensive than the traditional
one [42]. In few decades, an almost total conversion from handwritten to printed books occurred
[43]. Consequently, the materials also drastically changed: from the widespread use of the iron-
gall inks for handwritten documents to the almost exclusive use of carbon-based inks for printing
books. Moreover, the traditional variety of writing supports were replaced by mass-produced
papers. Notably researches were carried out on the Gutenberg Bible inks [44], [45], [46], [47]
and the on elemental analysis of ancient papers by Manso et al. [48], [49], [50].

With the aim of investigates this extremely rapid change, in 2018 in collaboration with Cà
Foscari University, we performed an extensive non-invasive investigation campaign of a large
corpus of early printed books. We analyzed inks and papers of sixty volumes, part of the
important collection of the Ateneo Veneto in Venice (Italy), printed between the 15th and the 17th
centuries in the main European manufacturing centers [15].



       X-ray analysis of inks

The ink chemistry of numerous manuscripts was analyzed using the X-ray Fluorescence (XRF),
a completely non-invasive and non-destructive technique widely used to investigate Cultural
Heritage objects [37], [39], [51]. As detailed reported in [9], I analyzed more than 20

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manuscripts’ - from a religious parchment to a 200-page physics book, from 16th century
documents to a modern mock-up.

Different points were analyzed for each manuscript, including the support – parchment or paper
– and several spots on inks. For the supports, XRF spectra confirm the light-element composition
with no features that could affect our analysis. For inks analysis, the XRF ink spectra were
corrected by subtracting those of the paper area. Although a full quantitative analysis is not
possible, this correction and the use of the same acquisition conditions allowed a good
comparison between data. In Figure 3 some examples of the XRF results on a 15th century
parchment (Figure 3a), and 1590 (Figure 3b), 1646 (Figure 3c), and 1664 (Figure 3d)
manuscripts. In inks, heavy or medium-heavy elements such as K, Ca, Fe, Cu, and Zn were
found. For the 15th parchment, the analysis detected Hg in the red ink (Figure 3a), most probably
cinnabar.

The spectra evidence two important issues. Firstly, the ink composition varies from ink to ink –
from an ink containing almost only a small amount of iron, as shown in Figure 3c, to those
containing several heavy elements such as the one of Figure 3d. Moreover, the investigation
revealed the high fluctuation in heavy-element contents, as illustrated in Figure 3b-c.

To better investigate this aspect, I compared the iron content of all the analyzed manuscripts –
as shown in Figure 4. As explained in detail in [12], the investigation highlighted the fluctuation
from manuscript to manuscript and does not show a clear time-related trend. Furthermore, the
comparison shown high fluctuations from page to page of the same documents (1590 and Phys
of Figure 4) and, more surprisingly, from words to words on the same manuscript pages (1679,
1797, 1801 of Figure 4). While the fluctuations between manuscripts, and maybe between pages,
are most likely due to different inks, the latter effects could have been caused by the handwriting
process itself, e.g., the variations of the rate of ink release by the pen.

These results pose one more challenge in the X-ray digitization approach: in the best situations,
the ink iron content is high, and the X-ray attenuation image quality is good enough to perform
the tomographic reconstruction of the writings. In the worst cases, even simple character
detection is a problem. But the fluctuation inside the same manuscript does not guarantee a good
visibility of the inks along with all the document.




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Figure 3: XRF analysis of ink and paper of a 15th century parchment (a), 1590 (b, 1646 (c) and 1664 (d)
manuscripts (Data from [9])




             Figure 4: Iron content detected by XRF in seventeen manuscripts over six
             centuries. The last six specimens were written after the mid-18th century and
             Modern is a simulated stack written with iron gall ink (Data from [12])




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To chemically study the early printing technology, to investigate its evolution and, potentially,
to identify physical/chemical fingerprints of different manufactures and/or printing dates, we
performed an extensive XRF campaign on sixty volumes, printed between the 15th and the 17th
centuries in the main European manufacturing centers [15].

Differently for the XRF analysis of manuscripts, the nature of these inks – mainly carbon-based
– and the low quantity of pigments left on the pages by the printing technique, made necessary
the development of a more sophisticated data pre-treatments to analyze the paper and ink
contribution independently.

As described in detail in [15], the analyses shown a high degree of homogeneity in all the
materials analyzed. The XRF investigations detected the use of carbon-based inks for all the black
features of the books, from the characters to the illustrations. Moreover, the ubiquitous presence
of small amount of K, Ca, Fe and Mn and the frequent presence of Cu and Zn were found. The
presence of elements such as K and Ca could be linked to the use of fillers, while for the other
heavy elements contain could be hypothesized the use of different ink recipes [44], [45], [46],
[47], or the transfer of particles from the metal types [48].

The papers’ analysis showed similar results, with the ubiquitous presence of small amount of K,
Ca, Fe, and frequently of Mn. Here, the presence of K, Ca, and Fe could be directly linked to
paper production: the K is linked to the Alum used as a mordant and Ca was used in all the
phases of the paper production, from the gelatin size to the whitening agents [48], [49], [50],
[52], [53], [54]. Moreover, traces of metals in water are likely responsible for Fe, and Mn
detection and an additional source could be identified in the particle transfer from the metal
types during the printing process [48].

Even if the results confirm the ineffectiveness of X-ray tomography as a digitization technique
for early printing books, the detailed statistical analyses identified potential fingerprints of
different European manufacturers, particularly the Venetian ones [15].



       X-ray imaging and tomography of ancient manuscripts

       Imaging with synchrotron radiation
To investigate the feasibility of X-ray imaging on manuscripts, I analyzed different contrast
mechanisms, i.e., absorption imaging and phase-related phenomena [55]. I performed the firsts
imaging experiments using a centralized synchrotron facility – the TOMCAT beamline of the
Swiss Light Source (SLS). This source allows an extremely high spatial resolution (some
microns), fast acquisition (some seconds), and imaging techniques with different contrast


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mechanisms such as free-propagation phase contrast and the differential phase contrast (DPC)
[56].

As described in detail in [9], the first experiment concerned the tomography of a bundle of eight
0.8 cm-diameter fragments of a 1679 specimen stacked together to simulate a small volume. In
Figure 5 the sample analyzed (Figure 5a), the two three-dimensional reconstructed tomographic
side views (Figure 5b), and the comparison between the visible picture of the fragments and the
tomographically reconstructed ‘pages’ (Figure 5c). The exceptional spatial resolution (6.5 μm
detector pixel) is largely sufficient not only to distinguish different ‘pages’ but also to determine
whether the writing is on the front or the back of each ‘page’.




Figure 5: X-ray tomography with a synchrotron source of a 1679 manuscript’s fragments (Data from [9])



To evaluate the capability of X-rays in detecting writings from different dates, the X-ray imaging
of three manuscripts from 1590, 1664, and 1801 are acquired and shown in Figure 6. As detailed
described in [9], images were acquired at TOMCAT with the free-propagation operation mode
and reflect both phase contrast and attenuation contrast. Here, phase contrast is primarily visible
in the microscopic substrate features, while attenuation contrast prevails in the ink areas.

Besides the iron X-ray attenuation contrast visible in each document – that made the manuscript
readable in X-rays - several other features almost invisible to the naked eye are identifiable. In all
documents, the X-ray imaging makes visible the high fluctuation in iron content detected by
XRF and proves that one of its causes is the ink released by the pen. Moreover, in imaging of
1664 manuscript (Figure 6b) the signs of corrosion of the paper by the iron gall ink are much
more evident than in naked eyes, and in Figure 6c the traces of the papermaking process are
perfectly visible as horizontal lines and emphasized by the phase-contrast mechanism.




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Figure 6: Comparison between visible picture and X-ray imaging with a synchrotron source of
manuscripts from different dates - 1590 (a&b), 1664 (c&d) and 1801 (e&d) (Data from [9])


In the case of low attenuation contrast, such as inks with a low iron content, the different imaging
techniques provided by synchrotron light could be helpful. This is the case of the DPC imaging,
where the acquisition process and the use of appropriate algorithms yield images corresponding
to different contrast mechanisms: absorption, scattering, and refraction [57].

In Figure 7 the imaging results of the 15th century parchment acquired in DPC mode at
TOMCAT [10]. In Figure 7b the DPC absorption-contrast image – equal to absorption
radiography – with the excellent attenuation contrast of Hg-containing red characters, and the
weak contrast of the black letters, in agreement with the low iron content detected by XRF (as
shown Figure 3).

Figure 7c and Figure 7d show scattering and refraction images. These seem to reflect the local
specimen morphology (the parchment topography) rather than only it’s chemical composition.
As described in [10], it is possible to argue that what we see in these figures corresponds to the
substrate morphology, probably related to parchment damages or differences in its thickness
(Figure 7c), and to modification of the more superficial features, apparently related to the writing
process or by the ink–substrate interaction. This could be used to detect a character when the
attenuation contrast would only give a very faint picture.




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Figure 7: Imaging with with different absorption methodology achieved with a synchrotron source. 14th
parchment in visible light (a), absorption (b), scattering (c) and refraction (d) (Data from [10])




       X-ray imaging with lab equipment

The success of the tests performed at a centralized synchrotron facility demonstrates the approach
feasibility but did not address two key issues: the needs of in situ analysis and the practicability
of the technique on large areas manuscript. The first is crucial since moving specimens to such a
facility creates conservative, logistic, practical, and even legal problems that would severely reduce
the impact of the approach. The second is strictly related to the first ones since synchrotron
emission is by its very nature highly collimated and typically used for small specimens. For these
reasons, a laboratory X-ray imaging facility is imperative for the development of X-ray
tomography digitization.

Initial imaging tests on large area manuscripts have been performed at the X-ray Imaging Center
of the Pohang University of Science and Technology (POSTECH) in Korea [11]. In Figure 8
the comparison of visible image and X-ray radiography of a single-page manuscript from 1679
acquired with laboratory equipment. The images show the excellent readability of the document
in X-rays. Moreover, demonstrate the system’s capability in detecting the ink-content fluctuation
and the effect of the intensity fluctuations due to the structures of the handmade paper and
invisible in the conventional visible imaging. As described in detail in [11], several other
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successfully imaging tests have been performed, such as tomography of a stack of different pages
of a modern manuscript created following ancient recipes – high-quality paper and iron-gall ink–
and imaging of an ancient book rolled up to simulate a multi-page scroll.

All the tests proved the feasibility of the X-ray tomography technique to read manuscripts also
with laboratory equipment, potentially available in situ and able to digitize large-areas
manuscripts.




Figure 8: Comparison of visible image (a) and X-ray radiography (b) of a 1679 manuscript achieved with
a lab-based source (Data from [11])

To evaluate the technique’s feasibility on large objects such as a large and thick manuscript, a
large handwritten scientific manuscript (27 × 19 cm2) by an Italian scientist, Giulio Mancini,
dated 1790–1800, was analyzed. The book consists of a 200-pages text with notes about different
branches of physics and includes several inserts with drawings and graphs.

The book was analyzed with different imaging facilities: the μCT instrument available at the
Center for X-ray Analytics at EMPA (Dübendorf, CH) [12] and the tomographic set-up of the
of X-ray Tomography for Cultural Heritage Laboratory of the University of Bologna [13].

The results shown in Figure 9 demonstrate the feasibility of the techniques with laboratory-based
equipment also for large manuscripts. Thanks to the 3D tomographic volume, we can visualize
the external part of the book (Figure 9b), and we can navigate through all the 200 pages, where
the writings are visible (Figure 9c). Moreover, the word reading is feasible, and Figure 9d shows
several examples of clearly readably individual words from inside pages.
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Nevertheless, the segmentation and extraction of the pages from these manuscripts are not trivial
and pose severe challenges for the segmentation algorithms. As shown in Figure 9c, the pages on
the book’s fore-edge are almost unrecognizable, making the segmentation really arduous. The
task is easier when significant air gaps exist between the pages and, in such cases, we can be
optimistic about the feasibility of unsupervised page extraction algorithms. For samples such as
this highly-compact book, the segmentation is extremely difficult, if not impossible with really
powerful            and             sophisticated          ad           hoc         algorithms.




Figure 9: X- ray tomography of a 200-pages book achieved with lab-based sources. Visible picture and 3D
image of the book (a), tomographic 3D image and view of the inside pages (c), words and drawing
extracted for the internal pages (d) (Data from [12] and [13])


In 2017, we performed a tomographic campaign of several closed and sealed last wills from the
Venetian Archivio di Stato. The Archivio contains thousands of testaments that are still
unopened: X-ray tomography constitutes the only chance to read them without breaking their
official seals. In Figure 10 the first result of the campaign: the tomographic imaging of a 1351
Venetian testament, a paper document (about 5x10 cm2), still sealed and folded six times. The
X-ray imaging were performed with the laboratory-based and transportable equipment of the X-
ray Tomography Laboratory for Cultural Heritage of Bologna University.

As shown in Figure 10b, the investigation detected words on the upper part of the external page
and the strongly absorbing effect of the wax seal on the verso of the manuscript. To analyze all
pages one-by-one, I performed a manual segmentation to separate the warped and closely-packed
individual pages. In Figure 10c, the individual segmented pages and, in Figure 10d, parts of the
texts and a complete internal page, extracted from the tomographic data.

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                                                        F. Albertin – X-ray tomography for manuscripts

Moreover, in X-ray tomography are readable the first lines of the external text: in Figure 10d
(left-top) the beginning of the document with a standard formula including the date, the place,
and the name of the recording officer. This external portion of the text gives the opportunity to
validate the tomography approach results, which reveals all pages equally well, internal and
external.

The X-ray tomography made visible for the first time in six centuries part of the internal text and
the first words of the document are perfectly readable: ”A nome de Dio” - ”In the name of God”,
a standard formula of the beginning of last wills – Figure 10d (left-middle). In Figure 10d (left-
bottom) many letters and several words from portions of internal pages are directly readable. In
Figure 10d (right) the reconstruction of the complete internal page, with lines of the text visible
and few words directly readable and others inferable.

The noise effect that disturbs the text reading is caused by the characteristic inhomogeneity of
the handmade paper. Also for this document are observable the contrast fluctuation from letter
to letter and between different parts of individual letters. These fluctuations, combined with the
noisy background, augment the difficulties of the virtual reading process. Moreover, it must be
taken into account that the document is written in ancient Venetian, and most of the words are
abbreviate - i.e. Venice was Rivoalti and written as Rti. This makes the reading of such documents
more difficult and non-trivial for non-experts.




Figure 10: Tomographic investigation of a 15th sealed Venetian document achieved with the lab-based
facility of UniBo. Visible pictures of the last will (a), 3D tomographic volume (b) and segmented pages
(c). In (d) portions of the internal pages and a complete page (d) (Data from [13])




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       Other imaging techniques

The VXR project proved the feasibility of the X-ray tomography and imaging of ancient
manuscripts wrote with heavy-content inks, in particular for closed and sealed ones. But
sometimes also the reading of open documents could be a challenge, such as in case of damaged
manuscripts, faded or smudged writings, or overlapped texts. For these cases, the use of imaging
techniques in the visible and near-visible light spectral range could be the key.

The visibility of inks and pigment is related to their absorption/reflectivity and these vary on the
spectral region analyzed. The use of an extended spectral range offers several advantages, such as
the increasing transparency of most of the pictorial materials as the wavelength increases (infrared
reflectography), e.g. resulting in better visibility of the preparatory drawing of the miniatures
thanks to the transparency of the overlaid pictorial layers. The use of the UV fluorescence
imaging technique stimulates the fluorescence of the materials and makes it possible to emphasize
details difficult to read – or hidden –in visible light. Moreover, preliminary considerations on
materials’ identification could be made basing on their different appearance in the different
spectral ranges.

Some examples of the behavior of inks in different regions of the spectra, part of the preliminary
study of the sixty early printed books analyzed and presented in [15], are shown in Figure 11,
Figure 12, and Figure 13.

In Figure 11 the imaging of a front page of a 1525 Venetian printed book in visible light (Figure
11 a), in the IR region (850 nm filter) Figure 11b), and under UV light to perform UV
fluorescence imaging Figure 11c). The front page is written in red and black inks and two
markers are present. While in IR imaging the black inks remain clearly readable, as well as the
markers, the red one disappeared. The behavior of the black ink used for the printed text suggests
the use of carbon-based ink. Indeed, while the iron-based inks are transparent to the IR radiation
the carbon-based inks are strong IR absorbers [58]. The high reflectivity of the red inks in the
IR region could suggest the use of pigment such as cinnabar, minium, or red lake [59] but the
imaging technique used is not adequate for its identification.

The UV fluorescence imaging, stimulating the fluorescence of the paper, revealed
inhomogeneities most probably related to humidity damages. Furthermore, a deeper observation
of the markers revealed some “smudges” near them, probably due to some organic components.

Similar inks behavior were observed for the imaging of an illustrated page of a 1485 Venetian
printed book shown in Figure 12. Here as well, the pigments - yellow and red - became
transparent in IR while the black text and illustration remain perfectly readable. Furthermore,
the UV Fluorescence highlight evident humidity traces.

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                                                        F. Albertin – X-ray tomography for manuscripts

The imaging analysis of a 1499 Venetian printed book shown in Figure 13 put in evidence the
behaviors of two different black inks: while the printed text and the illustration remain clearly
visible in IR, the manuscript annotations disappear. Again, this suggests the use of carbon-based
ink for the printed text and an iron-based one for handwriting [58].




Figure 11: Imaging in Visible Light (a), Infrared (b) and UV fluorescence (c) of a 1525 Venetian printed
book. (Data from [18])




Figure 12: Imaging in Visible Light (a), IR (b) and UV fluorescence (c) of a 1485 Venetian printed book.
(Data from [18])




Figure 13: Imaging in Visible Light (a), IR (b) and UV fluorescence (c) of a page of 1499 Venetian
printed book. (Data from [15])

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To analyze the inks used for early printed volumes, a XRF campaign was performed on the sixty
book.

In Figure 14 , the XRF results of the inks of Figure 11, Figure 12 and Figure 13 clarifies their
nature. The analysis of the red ink used for the colored title of Figure 11 detects Hg and Pb,
confirming the hypothesis made and suggesting the use of a mixture of Vermilion, and Red Lead.
A similar composition is found for the red ink of the illustration of Figure 12. The XRF of the
yellow ink detected As, Pb and Sn, indicating a combination of Lead-Tin Yellow and Orpiment
or Realgar. The investigation of the black inks of Figure 13 confirms the hypothesis of an iron-
based ink for the handwritten annotation and a carbon-based one for the printed text.




                    Figure 14: XRF analysis of the ink of Figures 11,12 and 13
                    (Data from [18])

The multispectral images presented investigate wide spectral ranges, impeding to take full
advantage of the different behaviors of the pigments in the different portions of the spectrum.

The use of techniques such as hyperspectral imaging allows exploiting these features to the
maximum [60].

This technique consists of acquiring and measuring the reflectance spectra of the analyzed object
in various wavelength ranges - usually in the range from 400 to 1000 nm in the visible and near-

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                                                     F. Albertin – X-ray tomography for manuscripts

infrared regions and using 50–150 different spectral bands. The result is an image cube, made
up of several images, each one corresponding to a particular wavelength band [60]. The analysis
and the reconstruction of the reflectance spectra of the pigments could allow their identification
[51] [59]. Moreover, in the case of pigments similar in visible light, the acquisition of tens of
“monochromatic” images enables their comparison in different parts of the spectrum and,
potentially, distinguishes them. Similarly, in the case of superimposed images or writings, could
be identified a spectral range in which the upper writing disappears, making the deeper readable.



       Conclusions

The research and studies conducted in the “Virtual X-ray Reading” framework, from the
extensive analysis of ancient inks to the radiographic and tomographic imaging of ancient
documents using synchrotron and lab-based equipment, demonstrated the feasibility of the
technique.

The iron-gall nature of the inks used for “every-day” manuscripts was tested by the extensive
XRF analysis performed along with the project and partially reported here. Furthermore, the
investigation highlighted one more challenge for X-ray imaging: the high fluctuation in heavy-
element content of the writings could make the X-ray contrast inhomogeneous along with the
texts. This, combined with the considerable inhomogeneity of the handmade paper, makes
essential a strong image pre-processing to improve the readability of the texts.

The imaging feasibility tests, performed both with synchrotron facility and lab-based equipment,
shown that the X-ray tomography of manuscripts and its reading is feasible, not only on small-
size objects but also on books. Nevertheless, a robust segmentation methodology is needed, and
its crucial for collection investigation, and it’s a formidable challenge.

Despite the challenges, the VXR project and its results proved that this approach is applicable to
the vast majority of European manuscripts and, potentially, to collections worldwide.



       Acknowledgements

I am grateful to Giorgio Margaritondo for his exceptional positive support and mentorship,
Patrick Aebischer for his leadership of the VTM project, and the Verbantiqua bookstore
(http://www.copernicum.it) for the generous donation of some of antique manuscript specimens
here presented. Over the years the project involved several Professors, Researchers, and
Laboratories and I am grateful to all of them. In particular, to the staff of the Swiss Light Source
for their technical support, to Professor Ferruccio Petrucci, Eva Peccenini, and Anna Impallaria

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of the University of Ferrara for their assistance in the chemical analysis, to Yeukuang Hwu and
Jung Ho Je for their support and for the analysis conducted at POSTEC, to the staff of EMPA
for their technical support, to the Archivio di Stato in Venice and its staff for their precious
collaboration, to the Ateneo Veneto for its essential help, to Dorit Raines for her extraordinary
support and mentorship, and the X-ray tomography for Cultural Heritage Laboratory of the
University of Bologna and its staff for the last years of working together.

The project was supported by the Ecole Polytechnique Fédérale de Lausanne (EPFL) under the
general framework of the Venice Time Machine Project, supported by the Lombard Odier
Foundation. Over the years, the researches were supported by various organizations: by the Fonds
National Suisse pour la Recherche Scientifique, by the Center for Biomedical Imaging (CIBM),
by the National Research Foundation of Korea (NRF), by the National Science and Technology
Program for Nanoscience and Nanotechnology, Taiwan, by the Thematic Research Project of
Academia Sinica (Taiwan) and by the MIUR National Access Pilot call (IPERIONCH.it,
IPERION CH Grant Agreement n. 654028).



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