Bronze Age painted plaster in Mycenaean Greece: a pilot study on the testing and application of micro‐Raman spectroscopy

Abstract

Since the first discoveries of Minoan and Mycenaean painted plaster around the end of the 19th and early 20th centuries, iconographic and, to a lesser extent, technological studies have gone hand in hand in order to understand how these prehistoric societies were able to produce some of the earliest and most significant works of art in Bronze Age Europe and the eastern Mediterranean. These paintings claim to be among the first to be executed in the buon fresco technique. Past technological studies employed wet chemical methods, x-ray diffraction (XRD), optical emission spectroscopy and a range of microscopic techniques based on cross-sections of samples in order to investigate these fragmentary paintings. Most of these methods required destructive sampling and this is now, rightly so, very much restricted. Consequently, other non-micro-destructive approaches are being tested at present. Micro-Raman spectroscopy (MRS) has proven more than once its potential for non-destructive analysis of works of art and in archaeology in the recent past. Its application to this early fragmentary material is presented here for the first time. Interesting results were the identification of both organic (indigo) and non-crystalline materials (limonite), which complements the knowledge obtained from traditionally used techniques. Although not without problems (high fluorescence prevented identification of Egyptian Blue), non-destructive MRS yielded results comparable to XRD and provided the first identification of indigo blue on this medium, and can hence be considered very useful in future sample-reducing strategies considering these scarce materials.

Pigment analysis in Bronze Age Aegean and Eastern Mediterranean painted plaster by laser-induced breakdown spectroscopy (LIBS)

“…Finally, the development and production of portable LIBS devices that would enable analysis on location are currently the subject of intense research as technological advances offer more and more options for compact laser sources and detection systems [72,21,63]. Obviously, the LIBS technique cannot completely replace other sophisticated (destructive) techniques but, as shown in certain cases, in combination with micro-Raman analysis [25,34,70] it can provide complete identification [17,19,69] for several organic and inorganic pigments, provided that the necessary reference libraries are present [5,17,15]. In the future, this combination may replace, at least partly, the traditional combination of XRD and SEMeEDS.…”

“…One could suggest that this may be caused by the presence of a mordant to fix an organic material as a pigment but this is rather unlikely considering the fact that virtually all painted plaster from the Bronze Age demonstrate a high level of al fresco painting with mainly mineral-based pigments. Where organic pigments have been identified such as black and indigo blue [12,15], these were applied in a clear al fresco painting technique. Another still unidentified purplish organic material (possibly Murex purple) from the site of Gla [16] has also been applied al fresco [13] which demonstrates that none of these materials needed a mordant or medium to be applied to the lime wall.…”

On‐site Raman study of artwork: Procedure and illustrative examples

“…Pigments were among the first materials to be studied when the first Raman Molecular Examiner (Mole) appeared in 1970s, [14][15][16] especially those used in illuminated manuscripts [16][17][18][19] or in wall paintings (frescoes). [20][21][22][23][24][25][26][27][28] However, those pigments generally consisted in powdered minerals with high purity, almost free of organic binders generating strong fluorescence. The sampling (a few square micrometres to a few square centimetres) and study was performed at a laboratory that allowed for the building of databases.…”

Painted plaster from Bronze Age Thebes, Boeotia (Greece): a technological study

“…Since the LIBS results agree with SEM and XRD results, I believe that it is no longer necessary to sub-sample all plaster samples for the identification of pigments. MRS, as a non-destructive technique (and now a portable instrument), is of equal importance in this context, but multiple laser beams and a complete reference database are needed to be able to analyse and identify all pigments (see Brysbaert and Vandenabeele, 2004). Since the ochre pigments in general have received adequate interest in the past, I focus here on the blue and purple samples.…”