article posted 22 March 2016
Fanny Alloteau graduated from Chimie Paris, specializing in Material Sciences. Since 10/2014 she is a PhD student at the Institut de Recherche de Chimie Paris. Thesis title: “Research for a protective treatment against atmospheric alteration of ancient glass objects”.
Zinc salts protection treatment for ancient glass objects showing atmospheric degradation in museums
Fanny Alloteau1-2*, Isabelle Biron2-1, Odile Majérus1-2, Patrice Lehuédé2-1 & Daniel Caurant1-2
1 Chimie ParisTech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris (IRCP), 75005 Paris, France
2 Centre de Recherche et de Restauration des Musées de France, PSL Research University, CNRS, Institut de Recherche de Chimie Paris (IRCP), 75001 Paris, France
A significant part of ancient glass in museum collections shows macroscopic signs of atmospheric alteration.1,2
Depending on the glass composition and the conservation conditions, the related mechanisms are not yet well deeply understood. Until now the best protective measure applied by conservators and curators to slow down the alteration is the control of the environment (temperature, relative humidity, pollutants). Nevertheless, by acting directly on the glass surface involving specific mechanisms with the glass structure, much more efficient protective methods can be proposed. Inspired by industrial process to protect manufactured glass windows during their storage and transport, we have recently highlighted the positive effect of a small amount of zinc salts to efficiently reduce the alteration kinetics of an alkali-lime silicate glass (figures 1 and 2).
With the final objective to optimize a zinc salts treatment for the museum context, the mechanisms underlying the atmospheric alteration as well as the protective action of zinc salts are studied by the mean of ageing experiments in climatic chamber (temperature and humidity control) on relevant chemically unstable ancient glass composition replicas. Polished glass plates and glass powders, with or without zinc salt deposition, are aged and characterized in terms of composition, morphology and structure.
Our results are in favor of an hydration mechanisms initiated by the diffusion of water molecules into the silicate network and their dissociation on some alkali bounded non-bridging oxygen atoms, producing hydroxide ions able to catalyse the silicate network hydrolysis.3 With a zinc salt deposit, zinc(II) on the glass surface precipitates with hydroxide ions : the pH of the hydrated glass surface is neutralized preserving the silicate network structure is preserved. Moreover, passivation effects are possible and research is currently carried out to put them in evidence.
(1) Koob, S. P. Atmospheric Deterioration of Glass: Crizzling. In Conservation and Care of Glass Objects; Archetype, U.K, 2006, 117-130
(2) Kunicki-Goldfinger, J. J. Unstable Historic Glass: Symptoms, Causes, Mechanisms and Conservation. Reviews in Conservation 9 2008, 47-60
(3) Alloteau, F.; Lehuédé, P.; Majérus, O.; Biron, I.; Charpentier, T.; Caurant, D.; Dervanian, A. A New Insight into Atmospheric Alteration of Alkali-Lime Silicate Glasses. 2016, Submitted