Evaluation of manganese-bodies removal in historical stained glass windows via SR-m-XANES/XRF and SR-m-CT† Simone Cagno, * a Gert Nuyts, a Simone Bugani, b Kristel De Vis, c Olivier Schalm, c Joost Caen, c Lukas Helfen, d Marine Cotte, e Peter Reischig d and Koen Janssens a Received 15th July 2011, Accepted 5th September 2011 DOI: 10.1039/c1ja10204d The speed and effectiveness of a conservation treatment used for stained glass windows have been investigated. Dark-coloured Mn-rich stains can be found in the alteration layer of ancient glass artefacts and cause the surface to turn brown/black: this phenomenon is known as Mn-browning or Mn-staining. While in glass manganese is present in the +II or +III oxidation states, in the Mn-rich bodies, manganese is in a higher oxidation state (+IV). In restoration practice, mildly reducing solutions are employed to eliminate the dark colour and restore the clear appearance of the glass. In this paper the effectiveness and side effects of the use of hydroxylamine hydrochloride for this purpose are assessed. Archaeological fragments of stained glass windows, dated to the 14 th century and originating from Sidney Sussex College, Cambridge (UK), were examined by means of synchrotron radiation (SR) based microscopic X-ray Absorption Near-Edge Spectroscopy (m-XANES) and microscopic X-Ray Fluorescence (m-XRF) and with high resolution computed absorption tomography (m-CT) before, during and after the treatment. The monitoring of the glass fragments during the treatment allows us to better understand the manner in which the process unfolds and its kinetics. The results obtained reveal that the hydroxylamine hydrochloride treatment is effective, but also that it has a number of unwanted side effects. These findings are useful for optimizing the time and other modalities of the Mn-reducing treatment as well as minimizing its unwanted results. Introduction Glass alteration is a complex process governed by several factors and involving various transformations; an overview of this degradation process was recently described in detail by us else- where. 1 The speed and nature of the corrosion process depend both on the characteristics of the glass (e.g., its composition, previous heat treatment, and surface roughness) and on external conditions such as microclimate, temperature, pH and compo- sition of the aqueous solution the glass was in contact with and the exposed surface area of the glass. Also, the corrosion process can be influenced by micro-organisms, air pollution, exposure to sunlight, traffic vibrations, and earlier conservation treatments. 2 The formation of brown-black Mn-rich corrosion bodies is one of the most disfiguring degradation phenomena that affect stained glass windows: a window pane that suffers from this phenomenon appears dark brown/black and completely lacks the transparency of the original glass. Mn-staining can appear both on archaeological glass and on in situ stained glass windows. Especially for stained glass windows reliable and harmless (for the glass and for the restorer) cleaning methods are highly needed. Two factors are crucial for this alteration process: the presence of water (vapor or liquid) and a source of manganese in the direct vicinity of the glass fragment or inside the healthy glass itself. While it is easily understood that the Mn can originate e.g. from the ground water that surrounds a piece of window glass buried in soil, the effect of ‘‘internal’’ Mn usually cannot be neglected. Historical glass often contains a small amount of manganese, usually between 0.4 and 0.8% w/w (when expressed as MnO). 3 The most important fraction of manganese in healthy glass is in the Mn(II) state (colorless), while a minor fraction may be present as Mn(III) (purple). Higher oxidation states of Mn are generally not present in fresh glass, since they are unstable during glass production (e.g. above 900  C). Mn can be introduced into glass in two ways: (1) as a raw material impurity (e.g., because it was present in wood ash) 4,5 and (2) because of a deliberate addition a Department of Chemistry, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium. E-mail: simone.cagno@ua.ac.be; Fax: +32 32652376; Tel: +32 32652363 b Department of Industrial Chemistry and Materials, University of Bologna, Viale del Risorgimento 4, I-40136 Bologna, Italy c Conservation Studies, Royal Academy of Fine Arts, Artesis University College of Antwerp, Blindestraat 9, B-2000 Antwerp, Belgium d Karlsruhe Institute of Technology, P.O. Box 3640, D-76021 Karlsruhe, Germany e ESRF, Rue Jules Horowitz, F-38043 Grenoble, France † This article is part of a themed issue highlighting the latest research in the area of synchrotron radiation in art and archaeometry. This journal is ª The Royal Society of Chemistry 2011 J. Anal. At. Spectrom. Dynamic Article Links C < JAAS Cite this: DOI: 10.1039/c1ja10204d www.rsc.org/jaas PAPER Downloaded by Universitat Hamburg on 11 October 2011 Published on 11 October 2011 on http://pubs.rsc.org | doi:10.1039/C1JA10204D View Online