Mobile Raman spectroscopy analysis of ancient enamelled glass masterpieces

Abstract

Richly decorated enamelled glass objects and fragments of different provenance and epoch have been analysed using mobile and fixed Raman instruments: some fragments of the outstanding Begram treasure (Musée des arts asiatiques -Guimet, Paris) dated to the 1 st century AD, mosque lamps and bottles of Syrian/Egyptian provenance dated to the 13 th /14 th century (collections of Musée du Louvre and of Musée des arts décoratifs, Paris). The techniques are compared using the data obtained from the study of a group of similar objects and fragments discovered in Melfi Castle in the South of Italy in an archaeological context dated to the last quarter of the 13 th century. The glass body was difficult to analyse requiring the use of high-energy high-power laser beams and/or sampling that allowed determining the soda-lime type precisely. In contrast, a variety of colouring agents was identified: lapis lazuli and/or cobalt for blue, antimonate pyrochlore solid solution for yellow, with the addition of cobalt/lapis lazuli for green, hematite for red and calcium phosphate/cassiterite/calcium antimonate for white. Where present, gilding was found applied on a rough and matt red enamel base probably in order to guarantee the physical adherence of the gold leaves. The comparison between the above mentioned groups of objects and between them and data existing in the literature about Roman enamelled glass allowed us to follow the evolution of the technology of this class of precious artefacts and to discuss the potential of the mobile Raman analysis.

Spectroscopic analysis used to uncover the original paint colour of the Helsinki Government Palace tower clock faces

“…Nowadays it is possible to say that the results obtained by in situ analysis are of the same quality as those obtained by laboratory instruments [12,13].…”

Natural Nanosized Raw Materials and Sol-Gel Technology: The Base of Pottery Since Millenniums

“…2 Examples of objects made using nanosized materials: a the formation of a glaze layer opacified with cassiterite SnO 2 precipitation gives a white substrate to make sophisticated décors, i.e. a pantheir or griffon in this Fatimids lustre pottery where the 'gold' colour arise from silver metal nanoparticles (Colomban 2004a); b this early Abbasids 3-colour pottery shows only SnO 2 opacification when the lead-rich Co-based blue or Cu-based green glazes react with the alkaline glaze covering the body (Colomban and Truong 2004); the very fine body is made from Euphrate nanosized alluvium; c the vivid blue of the Mameluk lamp [Louvre Museum (Caggiani et al 2013)] is obtained with lapis lazuli grains; d the blue décor of the Medici porcelain (Limoges Museum) is obtained with cobalt-based compound. In both later artefacts the white opacification results from calcium phosphates nanoprecipitates obtained from bone ash dissolution within the glaze (Berke and Wiedeman 2000) with composition homologous with that of Egyptian blue and green (Bianchetti et al 2000).…”

“…Attempts to imitate the Chinese porcelain were also conducted in Anatolia, but with a very different technology: Ottoman Iznik fritwares production peaks after 1450, and with the lack of white 'clay', the kaolin, they develop a white body by firing together sand quartz grains and lead-based frit, a low melting temperature glass (Atasoy and Raby 1989;Colomban et al 2004a;Simsek and Geckinli 2012). Actually the Ottoman potters created a very innovative material by applying a slip made of crushed quartz grains that reflect the light, enamelled the slipped body with a colourless lead-based glaze and developed advanced pigments and chromophores, especially by the use of multifiring procedure, as experimented for enamelled glass masterpieces during Roman times (Caggiani et al 2013). The use of a black non-stoichimetry phase (chromite and/or ferrite) to isolate glazed area lead to very sharp depicts.…”

Raman and SEM‐EDX analyses of the ‘Royal Portal’ of Bordeaux Cathedral for the virtual restitution of the statuary polychromy

“…However, nowadays, it is possible to say that the results obtained by in situ analysis are as good and have the same quality as those obtained by laboratory instruments. [19,20] It is true that laboratory instrumentation is, in general, well positioned in an airconditioned room, on a solid laboratory table, guaranteeing optimal alignment conditions and so on. When making a comparison with in-field instrumentation, one has to take into account that the recording of data under optimal conditions of samples is a very different approach than the recording of in situ data in non-ideal conditions (i.e.…”