Raman classification of the glass beads excavated on Mapungubwe Hill and K2, two archaeological sites in South Africa

About 200 coloured glass beads (red, yellow, green, blue, white, black, pink, plum) excavated on Mapungubwe hill and at K2, archaeological sites in the Limpopo valley South Africa, were studied with Raman scattering. This is also the most southern site in Africa where evidence for glass reworking has been found. The glass matrix of the beads was classified according to its Raman signature into three main subgroups and corroded glass could also be identified. At least seven different chromophores or pigments (lazurite, lead tin yellow type II, Ca/Pb arsenate, chromate, calcium antimonate, Fe–S ‘amber’ and a spinel) were identified. Many of the pigments were manufactured after the 13th century, confirming the presence of modern beads in the archaeological record. This calls for further research to find a way to reconcile the carbon dating of the hill, which currently gives the last occupation date on the hill as 1290 AD with the physical evidence of the modern beads excavated on the hill. The results are discussed in terms of the glass production origin of the beads (Europe, Mediterranean area, India, China).http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1097-4555hb2013ai201

A Raman spectroscopic study of glass trade beads excavated at Mapungubwe hill and K2, two archaeological sites in southern Africa, raises questions about the last occupation date of the hill

Thousands of glass trade beads were excavated over a 75 year period on Mapungubwe Hill and at K2, two archaeological sites in the Limpopo valley, South Africa. An assemblage of 175 beads that appeared to be different in shape, size and colour (red, yellow, green, blue, white, black, pink, plum) was studied with Raman scattering. At least seven different chromophores or pigments (lazurite, lead tin yellow type II, Ca/Pb arsenate, chromate, calcium antimonate, Fe-S amber and a spinel) have been identified. Pigment identification allows the recognition of specific productions and indicated that many of the pigments colouring the beads excavated on Mapungubwe hill were manufactured after the 13th century, confirming the presence of modern beads in the archaeological record, some dating from the 19th century. This date is in agreement with the last occupation date for the hill suggested by the earlier excavators and raises questions about the revision of this date to 1290 AD by archaeologists in the 1970\u27s

On-site Raman analysis of cultural heritage sites: the stained glass windows of the Sainte-Chapelle (Paris) and San rock art (South Africa)

Abstract of a paper that presented at XXII International Conference on Raman Spectroscopy, 8-10 August 2010, Boston (MA)

Raman classification of glass beads excavated on Mapungubwe hill and K2, two archaeological sites in South Africa

About 200 coloured glass beads (red, yellow, green, blue, white, black, pink, plum) excavated on Mapungubwe hill and at K2, archaeological sites in the Limpopo valley South Africa, were studied with Raman scattering. This is also the most southern site in Africa where evidence for glass reworking has been found. The glass matrix of the beads was classified according to its Raman signature into three main subgroups and corroded glass could also be identified. At least seven different chromophores or pigments (lazurite, lead tin yellow type II, Ca/Pb arsenate, chromate, calcium antimonate, Fe-S \u27amber\u27 and a spinel) were identified. Many of the pigments were manufactured after the 13th century, confirming the presence of modern beads in the archaeological record. This calls for further research to find a way to reconcile the carbon dating of the hill, which currently gives the last occupation date on the hill as 1290 AD with the physical evidence of the modern beads excavated on the hill. The results are discussed in terms of the glass production origin of the beads (Europe, Mediterranean area, India, China)

Origin of the variability of the mechanical properties of silk fibres: 3. Order and macromolecule orientation in Bombyx mori bave, hand-stretched strings and Nephila madagascarensis spider fibres

International audienceThe comparison of the low wavenumber of polarized Raman spectra (50–300 cm–1) from Bombyx mori (fresh cocoons fibres, hand-stretched ‘Crins de Florence’ strings from the gland content, dried gland, regenerated silk films) and Nephila madagascarensis silks reveals the high polarisation of fibre modes and the absence of polarisation for dried gland and regenerated silk films. This is consistent with X-ray diffraction measurements. The orientation of the fibroin/spidroin chains is due to the stretching during production, as for advanced synthetic fibres. The bandwidth of the ‘ordered chains’ signature is almost the same for the different fibres. However, the degree of polarisation seems to be higher in the case of spider fibre. The huge bandwidth of low wavenumber components of regenerated films indicates high disorder. Measurements along the fibre point out conformation changes with a periodicity (~20 mm) related to the silkworm head motion during the fabrication of the cocoon

Identification of Chromogenic Colour Photographic Print Brand by Fiber Optical Reflectance Spectroscopy and Statistical Analysis

International audienceOver the last quarter of the 20th century, chromogenic colour process was the predominant photographic process on the market and has been used by the professionals, artists and the public at large. Today it represents a precious part of our photographic heritage. Unfortunately, some colour prints are very fragile and discolour during display or storage faster than others; it is well known that some brands and production times correspond to different thermal and light-ageing behaviour for prints. Being able to identify a colour process, a brand and possibly a period of printing may inform us not only about the provenance of the artefact but also its sensitivity to the environment. With this aim, this paper investigates the possibility of using near-infrared spectral signatures of chromogenic colour photographs combined with statistical analysis to identify photographic paper manufacturers. To carry out the study, a batch of a few hundreds of amateurs colour photographs printed on Agfa, Fuji or Kodak paper produced from the 1960's to the 2000's was gathered from private and public collections. Non-invasive fiber optical reflectance spectroscopy (FORS) in the range of 1000–2500 nm was performed on those images in order to implement a reflectance spectra database. Then statistical data treatments were tested to evaluate the possibility of retrieving a print manufacturer with the lowest error possible. The use of linear discriminant analysis (LDA) combined with principal component analysis (PCA) allows reaching from 82 to 96% of correct identification depending on the paper type. This shows a possibility of implementing automated attribution procedures for chromogenic colour photographic prints

The first in situ Raman spectroscopic study of San rock art in South Africa: procedures and preliminary results

Southern Africa has a rich heritage of hunter-gatherer, herder and farmer rock art traditions made by using both painted and engraved techniques. Until now, there have been only a handful of studies on the chemical analysis of the paint, as all previous types of analysis required the removal of pigment samples from the sites a practice which has been avoided. Raman spectroscopy is an ideal techniques to analyse the paint non-destructively and also offers the possibility of in situ work with portable instruments. This article describes the procedures and reports the preliminary results of the first in situ Raman spectroscopic study of rock art in South Africa (also a first worldwide), where we, first, evaluate the capability of a Raman portable instrument in very difficult conditions, second, analyse the paints in order to contribute to a better knowledge of the technology used and, third, evaluate the possible contribution of in situ analyses in conservation studies. The paintings from two different rock art sites were studied. The instrument proved to be highly suitable for in situ analyses in physically very challenging conditions. Most of the pigments and alteration products previously detected under laboratory conditions were identified, thereby giving information on both the pigments and conservation state of the paintings. A layered structure of alteration products and pigment was identified in situ for the first time by controlling the laser power, thereby obtaining the same results as in mapping experiments of cross sections of paint

In search of the optimum Raman/IR signatures of potential ingredients used in San/Bushman rock art paint

Vibrational spectroscopy (Raman and FTIR) has played an important role in identifying pigments, substrata and deterioration products in rock art studies worldwide: in the laboratory and on-site. However, the detection of organic binders and carrying agents has so far been scarce and the quality of many spectra recorded on-site inadequate. In this study, possible pigments (charcoal, ochre, raptor faeces, thermally treated ostrich egg shell, etc.), binders (fat, egg, blood) and carrying agents (saliva, gall, egg, water) were selected based on artistic considerations and analysed with FTIR and Raman (514.6 and 785 nm excitation, both available in mobile instruments) spectroscopy in order to determine usable marker bands for each ingredient. The resultant marker bands were then used to analyse five ten year old San replica paints. It was found that FTIR spectroscopy is very efficient to identify organic compounds as there is no fluorescence but the broadness of the bands inhibits the exact assignment of many ingredients. A high fluorescence background experienced for many natural products prevented the recording of Raman spectra for all ingredients, in many instances though the sharp peaks usually associated with Raman spectra make identification easier than with FTIR spectroscopy. Most of the ingredients in the paints could be identified, but it is clear that better results are obtained when more that one technique is used

A multi-analytical characterization of French paper negatives: how to see through many processes?

International audiencePhotographic negative images on paper are certainly the earliest types of photographs ever produced, giving access to multiple prints of a same image using a unique matrix. As early as 1841 in France, many variants of the paper negatives processes have been developed by skilled chemists and photographers covering a wide spectrum of practical and aesthetic concerns. Nowadays, due to their inherent historical and esthetical values, those negatives are getting an increasing interest from the art and museum community. However their materiality has been less studied than positive images despite a large variety of processes and post-treatments involving many different chemicals and organic coatings; limiting our possibilities of identification, attribution or even preservation. The aim of this work was to develop a methodology to better assess the way those images were produced based on physical or chemical characteristics. A non-invasive approach combining optical, vibrational and X-Ray spectroscopies is implemented on a collection of 50 historical images between 1841 and 1860 from French collections. Working with non-invasive reflectance FTIR on such paper prints shows great potentiality in revealing the presence of organic coatings such as gelatin or wax. Besides, a survey is carried out on these negatives to provide a series of relevant dimensional and morphological data (dimensions, weight, paper texture, etc). The power of multivariate analysis is demonstrated first on each spectroscopic data set, and then using methods that combine data of different dimensions. With this effective statistical approach, it is possible to correlate the physical, chemical and dimensional characteristics to particular photographic practices, and highlight relationships between different makers