Inside the glassmaker technology: search of Raman criteria to discriminate between Emile Gallé and Philippe-Joseph Brocard enamels and pigment signatures Maria Cristina Caggiani, † Claire Valotteau and Philippe Colomban* The development of solid-state chemistry at the end of the 19th century offered a variety of routes to colour a glass matrix. Eight enamelled glass objects made by Philippe-Joseph Brocard and two representative objects made by Emile Gallé have been analysed using a mobile Raman instrument at the Musée des arts décoratifs (Paris) in order to compare their colouration technology. White, blue, yellow, green, orange, red, brown and black pigments have been identified. If most of the pigment palette is common to both craftsmen and typical of the second half of the 19th century, innovative uses are recognized for Gallé (wollastonite as an opacifier, manganese oxides in black mixtures) and Brocard (specific black and grey, pigment mixture, shade modification by small addition of white and red pigments). This preliminary work confirms the potential of Raman spectroscopy, not as a simple analytical method but as a way to document the ancient technology of fine art objects and to discriminate between different genuine productions and/or copies. Copyright © 2014 John Wiley & Sons, Ltd. Additional supporting information may be found in the online version of this article at the publisher’s web site. Keywords: glass; enamels; pigments; technology; Gallé Introduction Philippe-Joseph Brocard (1831–1896) is considered with Félix Bracquemond (1833–1914) as the founder of the modern glass- making art and craft in France. [1,2] The interest of P-J. Brocard for fine arts was large, and he had leading activity in the field of furniture, faience and glass. However, he did not produce glass bodies himself but developed enamelling and gilding technology, taking as model the most famous artefacts collected in museums. He is also well known for the restoration of many Mamluk Dynasty masterpieces. [3] Emile Gallé (1846–1904) was both a glassmaker and enameller, and his Art Nouveau produc- tion is well studied from the stylistic point of view. A series of books and exhibitions took place on the centennial jubilee (2004) of his death. [4–9] After working in the German Glass Factory, he visited P-J. Brocard in Paris and founded a workshop in Nancy that remained active up to 1936. [10] If the Brocard pro- duction is famous among glass scholars, that by Gallé captures the attention of a larger public, and fakes have been produced. The potential of mobile Raman spectroscopy [11] to identify in a non-destructive way the pigments as colouring agents and the glass/enamel composition of artefacts is now well established, for pottery, [12,13] glass [14–21] and metals. [22,23] During the 19th century, the development of chemistry offered a variety of new colouring agents, and craftsmen as painters tested the potential of these new chemicals. [16,24] It will be thus interesting to document the enamelling technology of the second half of the 19th century craftsmen in order to recognize specific Raman criteria of assignment to the production of specific workshops. The knowledge on enamelled glass is rather limited: Technical documents and recipe books are rare (e.g. in Colomban [24] ), and the number of studies is limited because of the fragility and high value of the artefacts. Sampling, including microsampling, is excluded because the thermal expansion mismatch between the body and the enamel matrix generates a compressive or tensile stress promoting the take-off of the enamel. For aesthetic reasons, most of the enamels deposited on glass should be opaque and thus may contain a large quantity of colouring agents, which makes Raman microscopy well adapted to the purpose. The combination with a mobile X-ray fluorescence (XRF) instrument [25] would have been highly complementary, but the XRF measurement requires a contact with the artefact, and only the very convex part of the artefact would have been accessible. In Raman microscopy, instead, the use of very long working distance microscope objectives allows analysing representative parts of the artefacts. We report here a preliminary study of representative artefacts with good pedi- gree belonging to the Musée des arts décoratifs: Most of the studied objects entered in the collection by direct purchase from Brocard or Gallé. [26] * Correspondence to: Ph. Colomban, LADIR umr7075 CNRS, Université Pierre et Marie Curie (UPMC), 4 Place Jussieu, 75005 Paris, France. E-mail: philippe.colomban@upmc.fr LADIR umr7075 CNRS, Université Pierre et Marie Curie (UPMC), 4 Place Jussieu, 75005, Paris, France † Present address: Dipartimento di Chimica, Università degli Studi di Bari ‘Aldo Moro’, Via Orabona, 4, 70125, Bari, Italy J. Raman Spectrosc. 2014, 45, 456–464 Copyright © 2014 John Wiley & Sons, Ltd. Research article Received: 27 December 2013 Revised: 10 February 2014 Accepted: 24 March 2014 Published online in Wiley Online Library: 30 April 2014 (wileyonlinelibrary.com) DOI 10.1002/jrs.4481 456