Journal of Cultural Heritage 19 (2016) 463–466 Available online at ScienceDirect www.sciencedirect.com Original article Investigation of ammonium oxalate diffusion in carbonatic substrates by neutron tomography Claudia Conti a,∗ , Chiara Colombo a , Giulia Festa b , Jan Hovind c , Enrico Perelli Cippo d , Elena Possenti a , Marco Realini a a Consiglio Nazionale delle Ricerche, Istituto per la Conservazione e la Valorizzazione dei Beni Culturali (ICVBC), Via Cozzi 53, 20125 Milano, Italy b Università degli Studi di Roma Tor Vergata, Dipartimento di Fisica, Via della Ricerca Scientifica, 1, 00133 Roma, Italy c Paul Scherrer Institut, Spallation Neutron Source Division, Neutron Imaging and Activation Group, 5232 Villigen PSI, Switzerland d Consiglio Nazionale delle Ricerche, Istituto di Fisica del Plasma (IFP), Via Cozzi 53, 20125 Milano, Italy a r t i c l e i n f o Article history: Received 15 September 2015 Accepted 4 December 2015 Available online 11 January 2016 Keywords: Neutron tomography Stone materials Product diffusion Ammonium oxalate a b s t r a c t The diffusion of the organic-polymeric or inorganic-mineral products inside a decayed porous material is a key factor for the evaluation of the efficacy of a conservation treatment. Here, we present a study aimed at the evaluation of neutron imaging as a non-destructive tool for the investigation of stones treated with ammonium oxalate, an inorganic-mineral product. Neutron tomography gained an overview of products diffusion and deep insight into the interaction between product and crystalline matrix. © 2015 Elsevier Masson SAS. All rights reserved. 1. Introduction For several years, the conservation scientists have been work- ing to find the most suitable methods to evaluate, in a direct way, the diffusion of a treatment in a porous material. Several analytical techniques have been proposed as staining tests, micro- ATR (attenuated total reflection) spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectrometry, X-ray photoelectron spectroscopy, micro-Raman mapping and drilling resistance [1–6]. Even though interesting results have been achieved, these tech- niques are destructive and they are unable to provide an overview of the treatment diffusion inside the sample in its entirety. In order to make up for this lack of information and to find a non-destructive method, an alternative solution is here pro- posed: neutron imaging, an emerging method for cultural heritage investigation, which provides complementary information to the corresponding X-Ray techniques. Due to their charge neutrality, neutrons can penetrate thick samples showing hidden details past outer corrosion and/or buried layers into bulky objects. Neutrons interact significantly with light elements, and in particular they are mostly scattered by hydrogen, giving detectable image contrast. Such circumstance candidates the neutron imaging as a possible ∗ Corresponding author. Tel.: +39 2 66 17 33 37; fax: +39 2 66 17 32 96. E-mail address: c.conti@icvbc.cnr.it (C. Conti). tool to determine the water absorption and distribution inside the material, identify the content and the penetration depth of hydrogen-rich conservation products (as in the case of organic treatment) inside porous stone samples or other materials such as bricks or wood [7–11]. To the best of our knowledge, no findings exist in the litera- ture concerning neutron imaging applied to the detection of the diffusion of fully inorganic treatments, although there is a strong increase of their employ in the conservation works, while it has been used for the investigation of ethyl silicate distribution [7]. Therefore, the aim of this study is to extend neutron imaging to the study of inorganic-mineral conservation treatments, obtain- ing the overview of ammonium oxalate [(NH 4 ) 2 (C 2 O 4 )] diffusion inside a building stone; the occurrence of hydrogen in the compo- sition of the newly formed minerals supports the hypothesis of a different neutron absorption of the treated portions compared with the untreated ones, made out of a stone almost completely wanting in hydrogen. The experiments have been carried out at the Paul Scherrer Institut (PSI) spallation neutron source (Switzerland). 2. Materials Neutron tomographies were carried out on Noto stone speci- mens (5 × 5 × 1 cm) treated with ammonium oxalate (NH 4 ) 2 C 2 O 4 , an inorganic-mineral product. http://dx.doi.org/10.1016/j.culher.2015.12.005 1296-2074/© 2015 Elsevier Masson SAS. All rights reserved.