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However before analysis can be made, there needs to be a reliable set of reference samples of pigments, inks, resins, binders and so on, from relevant periods, that can then be used for the interpretation of analysis data-sets. Using these reference graphs for comparison, it is possible to identify the pigments used in a work of art without the need for invasive techniques to obtain samples for chemical analysis. This provides valuable data for authenticity and provenance investigations as well as knowledge of the pigments used by the artist.
The Kubelka-Munk Equation connects light reflectance scattering to absorption in effectively opaque materials, such as paint on canvas.
Researchers found that hyperspectral data taken in the visible to shortwave infrared — nm produces FORS quality spectra for the complete surface of the painting and could be used to separate, identify and map pigments. A great deal of valuable information about the intentions of the creator of an artwork, such as changes made during the creative process, alterations and the manner in which the artist worked, can be determined from the examination of underlying drawings, sketch lines and work that was eventually painted out. X-ray technology has been used for this purpose [6] , but has limitations — for example charcoal sketch lines on dark backgrounds cannot be distinguished.
Hyperspectral imaging offers the possibility of seeing more clearly through surface layers. Light penetration is a function of wavelength.
This is shown by the Beer-Lambert Law, demonstrating that penetration is inversely proportional to wavelength. This means that since ultraviolet light has a shorter wavelength it will penetrate further through paint layers to reveal what is below. While single-wavelength data can be of some value, hyperspectral imaging permits a dramatic increase in information since data from across the full waveband can be simultaneously displayed.
Using image visualization software to process the data cube, the reflectance at each point and wavelength can be expressed in its principle components PCs. These can be converted into gray-scale images. By removing the main PC, lesser values are revealed, which show, for example, sketch lines, and even enable discrimination between charcoal lines and ink lines. In a study at the Winnipeg Art Gallery, Canada, a 15th century drawing, Untitled The Holy Trinity by Viet Hirschvogel the Elder, was analyzed using hyperspectral imaging equipment, to reveal not only the lead-pencil outline used for the drawing sketch, but the several different inks used to create the base for the actual drawing.
False color infrared reflectograms showing three detailed sections from The Tragedy. Each image shows a selection of the spectral bands that best reveal the various underdrawings and caricatures on the panel. Left: Drawing for the man , , nm; Middle: Horse , , nm; Right: Sketches , , nm. Delaney et al.
Therefore, the combination of reflectance spectra and narrow band false color composite images improve the ability to emphasize features of interest when compared to the earlier methodology. The versatility of hyperspectral imaging means that three-dimensional objects can also be analyzed.
These could then be compared to the results from a sample of the original Carrara marble used to create the work. Some areas showed variations from the Carrara signature, indicating where repairs had been made. Renaissance artists used a variety of materials to bind their pigments and often different materials were used with different pigments in the same painting. Reference samples of the most common materials, animal skin glue and egg yolk, could be matched using near infrared hyperspectral imaging to specific areas of the painting and to specific pigments.
The objects do not constitute a coherent group of finds in the archaeological sense: the group was acquired through individual purchases arising during the trip in Tunis, for example, duplicates in the Museum collection were offered for sale. Ferenc Hopp never intended these objects for his own collection.
In one of his letters he gave orders to ship the boxes containing the objects straight on to the National Museum without even opening them. Hopp, a lover of Oriental art, was indifferent to Greek and Roman antiquities. Even though the turn of the 19th and 20th centuries was one of the high points in the history of the international antiquities market, Hopp on his Italian trips bought himself modern imitations instead of genuine ancient marbles.
The person who bought antiquities in Sicily and Carthage was not the collector but the citizen. While the collector was not interested in ancient art, the citizen could not remain indifferent when the opportunity arose, and seized it in order to enlarge a public collection.
What is more, he was working, as the passage above attests, more probably on his own initiative than on the Museum's behalf. He purchased a rich collection of objects - not very costly, but at his own expense - for donation to the Hungarian National Museum.
It shows his modesty that he devoted only one sentence to the whole episode in his memoirs A Winter Journey Through the Countries Around the Mediterranean Sea , The two main motives of donors, a desire for fame and the inspirational force of personal taste, are both absent in his case.
These antiquities testify to an uncommonly selfless and modest patron of the arts. It was this very modesty, and the scanty information surviving about the purchase, which until very recently prevented any effort to reconstruct the real scope of Hopp's acquisitions. Contrary to what we would expect today, the objects were deposited in the Ethnographic Collection of the National Museum the forerunner of today's Museum of Ethnography rather than its Archaeology Department.
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Under the terms of the Museums Act, which defined the scope of the various Hungarian national museum collections, the majority of the pieces were gradually transferred in the course of the twentieth century to the Museum of Fine Arts. This process concluded in , when the Museum of Ethnography, with a generosity worthy of the donor, transferred a further 51 objects identifiable as having belonged to the Hopp collection. Today the collection is kept in the Collection of Classical Antiquities.
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Introduction 2. Greek Transmission OG 3. Greek-Arabic Transmission OA 3. The Context for Textual Transformation 4. Alternative Conceptions of Geometric Optics 4. Problems with Euclid 4. Criticism in Late Antiquity 4.