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Theradiography of cultural property is the use ofradiography to understand intrinsic details about objects. Most commonly this involvesX-rays of paintings to revealunderdrawing,pentimenti alterations in the course of painting or by later restorers, and sometimes previous paintings on the support. Manypigments such aslead white show well in radiographs.
X-ray spectromicroscopy has also been used to analyse the reactions of pigments in paintings. For example, in analysing colour degradation in the paintings ofVincent van Gogh.[1]
These processes can reveal various details about objects that are not visible to the naked eye. This information, which includes structural elements, aidsconservators as they assess object condition and consider treatment plans.
For three dimensional objects, thecomputed tomography (CT) has become a common tool, which when combined with analysis can, for example, "digitally unroll" or unfold and make possible the reading of fragile scrolls, books, orsealed correspondence.[2]
Infrared andultraviolet light are also useful tools to understand the intrinsic details of certain objects. However, X-rays tend to be more useful for denser objects.[3] The benefit of radiography is that it is not intrusive. Radiography does expose the object toradiation, but these levels are low. In fact, they are much lower than the radiation levels required for medical X-rays. While technicians and staff conducting the X-ray must use protective gear, the object is not damaged during the process.[4][5] Furthermore, the use of radiography is widely accepted by conservators, art historians, and archaeologists.[5] Several institutions around the world conduct radiography of objects in their collections including theVictoria & Albert Museum in London, England and theSmithsonian, which operates theMuseum Conservation Institute.
Conservators and art historians have used radiography to uncover technical information about paintings. Compositions of materials, previous alterations, and painting techniques have been revealed in X-rays.[6] This data has also been used to date works and identify forgeries.[7] Diagnostic and therapeutic X-ray systems are generally used to produce X-rays of paintings.[8] Infrared reflectography has also been used to seeunderdrawings and previous markings on painted canvases.[9]
Paints are produced with a variety ofelements. Depending on how much these pigments absorb X-rays affects how clear or opaque they will appear in the radiograph, this is known as X-rayfluorescence.[4][10]Lead white, for example, will absorb more rays and appear much more opaque on an X-radiograph thancarbon black, which will allow most of the X-rays to pass through resulting in a clearer result on the radiograph.[4][11] To produce a radiograph of a painting, the radiographic film is placed on the painted surface and the X-ray tube is placed behind the canvas.[12][4]
An X-ray of theGhent Altarpiece, painted byJan van Eyck, inSaint Bavo Cathedral in Ghent,Belgium revealed the structure and details of the large altarpiece's painting scheme. The complete radiography of thealtarpiece was conducted between 2010 and 2011 as part of a project largely funded by theGetty Institute. The X-rays and other technical information that was gathered were used to prepare conservation treatments.[13]
The Sampling Officials of the Amsterdam Drapers' Guild, also known as theSyndics of the Drapers' Guild or more simply as the Syndics, was painted byRembrandt in 1662. An X-ray of the painting revealed that Rembrandt fine-tuned the composition several times, alternating the glances between the figures and slightly changing their positions before he settled on that is known today.[14]
X-ray analysis revealed alterations to the paint of a sixteenth century portrait that had been identified as aBronzino portrait ofEleanor of Toledo at theCarnegie Museum of Art inPittsburgh,Pennsylvania. After a conservation treatment, which removed the added paint, the subject of the portrait was found to beIsabella de' Medici. The painting was also attributed to Alessandro Allori.[15][16]
Jean-François Millet's The Wood Sawyers atVictoria & Albert Museum was X-rayed, revealing that Millet had reused a canvas to complete this oil painting. The artist not only painted over a previous work, but he had also added strips of canvas to enlarge the painting area.[7]
According to X-rays taken of Twilight byJean Baptiste Camille Corot, also at the Victoria & Albert Museum, the artist painted over a previous picture that had not even dried yet. Pigments from the lower painting appear through cracks in the surface layer.[7]
The Old Guitarist byPablo Picasso at theArt Institute of Chicago had been previously examined with visible and ultraviolet light, which had hinted at the possibility of an earlier composition. X-rays of the painting revealed that Picasso had originally painted two female figures behind the guitarist. The X-rays also penetrated far enough to reveal how Picasso had prepared the wooden panel for painting.[8]
X-rays can provide a better picture ofplaster casts and other works that rely on internal supports. However, size and mobility can often affect whether or not radiography is an option for sculptural works. X-rays can also identify cracks and previous repairs toglass andceramic materials, which is important for assessing the condition.[4] This information can also reveal details about the manufacturing process, which may be instrumental in providing establishing place of manufacture, and possibly also revealinherent vices that are not visible to the naked eye.[5]Jewelry and other objects withinlaid pieces have been X-rayed to reveal more about their structure.[6]
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The plaster cast ofMichelangelo'sDavid at the Victoria & Albert Museum was X-rayed revealing that the supports in David's legs were positioned similarly to that of bones in a human leg. The size of this particular piece required a portable machine to complete the X-rays.[17]
TheMuseum of Applied Arts in Vienna, theResearch Centre Seibersdorf [de], and theNew York Historical Society have used X-rays to learn more about the manufacture ofArt Nouveau styleglass. In particular, they are investigating differences betweenTiffany glass of New York and Austria's Loetz glass to learn more about differences in the manufacturing process.[18]
In the X-rays of a wooden power figure at theIndianapolis Museum of Art, conservators discovered that there were hollowed out sections through the center of the sculpture that connected three filled cavities. Information about the network inside of these sculptures has aided curators as they research the function of these pieces. The findings have led to the use of radiography to compare power figures in other collections.[19]
X-rays can reveal information about layers oftextiles and stitching patterns. Forquilts, for instance, different textile types and other materials are used.[20] These materials are often hidden in the finished quilt. Therefore, X-radiography can provide conservators with useful information. For other textiles X-rays can also provide conservators with information aboutdyes since metallic mordant has historically been used in the dye making process. Details about stitching patterns can also appear on X-rays.[20] The Victoria & Albert Museum has used X-rays as a tool for several textile conservation projects.
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X-rays of theKing George III Golden Jubilee Quilt from 1810 revealed concealedstitching patterns and fabric dyes.[20]
Conservators learned more about the complex stitching of the Sundial Coverlet, which dates to 1797, through X-rays.[20]
X-rays were used to understand some of the stains and stitching patterns on an Egyptian tunic, dating to AD 600–799, in the Victoria & Albert collection.[21]
Hidden design and structure details were visible on X-rays of pairs ofshoes in the V&A's collection.[22]
Archaeological materials have also benefited from X-rays. X-rays of soil segments have revealed artifacts that have eroded away, leaving them nearly undetectable to the naked eye.[23] Worn and damaged surfaces, which appear unmarked, have yieldedinscriptions or other markings on X-rays.[24] Heavily corroded metal objects have also used X-rays to learn more about their original state.[5] Industrial and medicalCT scans have also been used by archaeologists to study a variety of artifacts.[25][26][27]Underwater archaeologists have utilized X-rays to see what is beneath layers ofconcretions.
Radiography has been used with human dry bones to diagnose pathologies, demonstrate trauma and assist age estimation through dentition eruption status.[28]
X-rays have been employed to analyze what is under the wrappings ofmummies.[26] In addition to providing images of the bones within, X-rays have revealed the location of jewelry and other objects that were buried with the body without disturbing the wrappings.
TheHerculaneum papyri that survived theVesuvius disaster were excavated and researchers have used X-rays to read their contents. Previous methods involved slowly unrolling thepapyrus, which damaged much of thescrolls, some beyond repair.[29]
X-ray technology was used to quickly identify individualcoins uncovered in a single container. Researchers did not have to wait for slower, traditional conservation methods to separate and decipher the coins.[30]
X-rays were among the imaging techniques used to uncover lost text on theArchimedes Palimpsest, which is in the collection of the Walters Museum in Baltimore, Maryland. The museum spearheaded an extensive research project on the palimpsest that employed various imaging techniques including ultraviolet, infrared, and X-radiography.[31]
The heavily corrodedAntikythera mechanism, which was uncovered from a shipwreck at the beginning of the 20th century, has been X-rayed several times in an effort to understand how it works.