These accounts include descriptions of some less familiar methods, such as xeroradiography, stereoradiography and the application of recenty introduced image processing techniques. They demonstrate vividly the versatility of radiography, and the range of topics discussed illustrates the valuable contribution that radiography can make to the study of artfacts made from a variety of materials, from many different cultures.
For the most part, the book is arranged on the basis of the nature of the materials studied; the particular concerns of the conservator are then consdered, followed by a discussion of the use of radiography in the detection of restoration, pastiche and fakes. The final chapter provides an account of the application of computer-based image processing techniques. Written by experts in their particular fields Of interest to the conservator and curator alike Illustrated with over photos and line drawings. Article Google Scholar 3. Article Google Scholar 4. Article Google Scholar Download references.
Schofield Authors Search for Eleanor J. Ethics declarations Competing interests The author declares no competing interests. Additional information Related links Mary Rose Trust: www. Rights and permissions Reprints and Permissions.
Radiography of cultural objects - Wikipedia
About this article. Cite this article Schofield, E. Further reading Transient absorption spectroscopy using high harmonic generation: a review of ultrafast X-ray dynamics in molecules and solids Romain Geneaux , Hugo J. Marroux , Alexander Guggenmos , Daniel M. Leone Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences Influence of microstructure on the corrosion of archaeological iron observed using 3D synchrotron micro-tomography H.
Simon , G. Cibin , C. Reinhard , Y. Liu , E. Harding Heritage Nature Reviews Materials menu. About the Journal Contact For Referees. The scale bar for b reports the values of the absorption edge jump, defined as the difference between the average intensity value in the XANES postedge region and the average intensity value in the XANES pre-edge region.
Radiography Cultural Material
The scale bar for the maps shown in c indicates the energy of the absorption edge in eV. The study of the iron speciation needs a further analysis since it requires the use of the whole XANES spectrum and not only two parameters height and energy position of jump edge deduced from this spectrum. The number of pixel spectra is too huge close to 2 millions to consider an individual treatment.
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TXM-Wizard software proposes two approaches for a closer inspection of the set of XANES spectra: i a principle component analysis PCA followed by a k -means clustering or ii a least squares linear combination LSLC fitting with standards associated to a R-factors correlation analysis [ 11 ]. The first approach allows us to obtain a first result with open-minded solution.
Here the PCA results show that the first four components Figure 3 allow a rather good system description. Indeed, the first two components represent already a percentage of The first cluster includes all the XANES spectra related to the coating, while the other clusters correspond to the body Figure 4b. A few differences can be observed between the external top and internal bottom coatings.
In the two cases, the hercynite concentration is higher in the upper part of coating close to the surface , but the external coating exhibits a clear reoxidation of its surface, which is marked by the presence of a thin maghemite layer at its surface. The trichromatic phase map, excluding hematite, is shown in Figure 6a and compared to the map obtained for a Campanian ceramic fragment of Roman period. The detailed analysis for this last case can be found in Ref. Result of PCA analysis showing the contribution of the first principal components highlighted in blue color.
The references of hercynite, magnetite, and maghemite are taken from ALS database.
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Phase maps obtained from the least squares linear combination fit of reference XANES spectra for magnetite, maghemite, hercynite, and hematite for each single pixel. The coating of Campanian contains mostly hercynite with only a few amount of maghemite mainly located at some surface areas, while the coating of Attic contains both hercynite and magnetite. These differences do not come from small variations in chemical composition between these two types of potteries, made at different places and times from similar but, however, different raw materials. They are actually due to the firing conditions.
The coating has a lower glazing temperature than the body and thus is also glazed during this step. Then, during this last step, the body is mainly oxidized and turns red. On the other hand, the presence of maghemite in some areas of the coating indicates that the chemical reaction between the coating and the kiln atmosphere was stronger during the last step. Maghemite is not distributed in a thin surface layer as in the exterior Attic coating but it is distributed in depth in some localized areas. The amount in these areas is also higher.
This feature seems to be due to worse glazing of the Campanian coating. Coatings are made from the fine part of raw clay, and the selected part for the elaboration of Attic coating was finer than for Campanian as revealed by quartz crystals sizes. Also, even if the two coatings have close elemental compositions, the glazing temperature of Attic coating is lower. The use of less fine part with larger grains of sand mainly quartz increases the porosity of glazing coating and then enhances its oxidation rate under the oxidizing atmosphere of kiln.
The presence of hematite in the Campanian body is consistent with an oxidation at higher temperature allowing a partial transformation or recrystallization of maghemite into hematite. The hercynite-rich zones of Campanian body correspond to partially glazed zones, which did not be therefore completely reoxidized during the last step.
The differences are only related to the characteristic differences between the two beamlines, that is, a smaller FOV and a better spatial resolution about one order of magnitude at Stanford. In the problematic presented here, the better resolution does not bring much more in the iron speciation study and the larger FOV of ID21 shows a best advantage.
On the other hand, the very good resolution of c beamline allowed for studying the sample porosity and for showing that hercynite was distributed in well-glazed dense zones. A study of a presigillata fragment was also carried out at SSRL [ 13 ]. This type of pottery, which was also made during the Roman period but a century later than the Campanian productions, presents also a glazed black coating covering a red body.
The results revealed both a high concentration of hercynite in the coating and a significant rate of hematite in the body. The top layers of the coating showed also a strong reoxidation with a significant presence of maghemite at the surface. To conclude with this explanation of the problematic, a few words will be given on a recent study, which suggests that more complex firing protocols would have been used for some Attic productions [ 16 ]. Paul Getty Museum showing as well the actual possibility to use this technique to study precious samples.
The analyzed fragment presents in some areas a red coating under the black coating [ 16 ], Figure 1. FF-XANES investigation revealed that this red intermediate coating contained mainly hematite, while hercynite and maghemite were found in the black coating and the body, respectively [ 16 ], Figure 2. The massive presence of hematite in this intermediate coating, whose chemical composition and the porosity are identical to the ones of black coating, was not considered as consistent with the firing protocol proposed by Noble.
This firing protocol would have led to the same mineral composition for the two coatings. Also the authors proposed a more complex protocol involving two separate firings. In the first example, the average elemental composition and the concentration of the selected element, in this case iron, were quite suitable to transmission mode measurements. This technical analysis can be also successfully used to study the speciation of an element in low concentration with, however, some restrictions as described in this second example.
Blue and withe porcelain Figure 7 , so-called Qinghua porcelain, is characterized of a brilliant white translucent glaze with a blue pattern painted underneath. The color is due to cobalt, but other transition metal elements including iron and manganese are also present in the Ming productions [ 17 ] and the aim of study was for establishing the feature of each [ 18 ]. The thin parallel-faced blades were made as previously described cf. Section 3. Unfortunately with such a thickness, the absorption of these other elements Al, Si, K, and Ca limits the transmission in the energy range to a few percent and does not allow measurements in transmission mode.
A sample ready for investigation is shown in Figure 8. For the preparation method, refer to Figure 1. X-ray absorption spectra XAS collected in fluorescence mode are better suited for determining the speciation of elements in low concentration [ 19 ]. Unfortunately, the scanning of a large zone with a submicrometric resolution is too time-consuming for analyzing even a few samples.
Also the technical advantages of the two techniques were combined.
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At first, XRF maps were collected in scanning mode on large areas. The PyMca software was used to batch-fit the XRF spectra, to generate the elemental maps from Na to Co and to normalize these maps taking into account the incident beam intensity [ 10 ].
A typical result showing the main differences of elemental distribution in the various layers of a Ming Qinghua porcelain is presented in Figure 9. The colored zone is clearly identified by the high rate of calcium. The localized high concentrations in silicon correspond to quartz grains, which are more numerous in the body than in the glaze.
The needle-shape crystals observed in the colored zone containing calcium are anorthite crystals [ 20 ]. The distribution of three transition elements Mn, Fe, Co is quite different. Mn and Co distributions are concentrated in colored areas confirming there are well contained into the pigment. However, Mn distribution is more uniform and does not present local high level compared to Co element. Fe is quite homogeneously distributed both in colored area and in above glaze. Laboratory XRF measurements revealed that the glaze areas without blue decors contain similar Fe rates [ 18 ].
A few punctual XANES spectra were acquired at the Co K-edge both over Co-rich particles and diluted Co in glassy matrix, by scanning the energy of the incoming beam and measuring the X-ray fluorescence signal of Co K-lines.