Gypsum based mixes for conservation purposes: evaluation of microstructural and mechanical features

V Brunello,A Sansonetti,C Tedeschi,L Rampazzi,D Bersani

doi:10.3989/mc.2020.05019

Abstract

This paper presents the study of four gypsum mixtures, focusing on the role of both inorganic and organic additives and on the micro-structural features and mechanical properties. Additives have been chosen among those most reported in historical recipes, for example magnesia, lime putty, rabbit glue. The selected mixes refer to gypsum-based materials used in artworks manufacture, such as plasters, mouldings, stuccoworks, pastiglia. Blank reference materials were prepared on purpose according to the specific recipe, in order to verify the final composition and to highlight the hardening mechanisms and the formation of setting compounds. The chemical composition was related to workability properties and final mechanical resistance and the action of additives as retardants was studied with interesting results. For instance, MgO imparts good properties to the mechanical features, especially with regard to the compressive strength characteristics.

Highlights

This paper presents the study of four gypsum mixtures, focusing on the role of both inorganic and organic additives and on the micro-structural features and mechanical properties
It is worthwhile to note that magnesium oxide and calcium carbonate have been detected in recent characterisation studies [9, 11, 13, 28, 45], as well as animal glue or other protein based materials [11, 41]
The characterization of the raw materials and of the mixtures was carried out combining mineralogical (X ray diffraction) and spectroscopic analyses (Raman Spectroscopy and Fourier Transform Infrared spectra (FTIR))

Summary

Introduction

This paper presents the study of four gypsum mixtures, focusing on the role of both inorganic and organic additives and on the micro-structural features and mechanical properties. Gypsum based materials were utilised in plastering and rendering, bedding mortars, stuccoworks and some outstanding decoration techniques of small artworks, such as pastiglia This Italian term recalls a low-relief decoration present in several early Renaissance caskets, paintings and frames, with gilt or painted finishes. For example low and high reliefs, mouldings and in the round statues implied the workability properties of the mixes used For these reasons gypsum was often mixed with both organic and inorganic natural and artificial materials, such as lime putty and organic additives [8,9,10,11,12,13,14,15,16,17,18,19,20]. According to the literature there are still doubts about the transition conditions between one phase and the [31,32,33,34]

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Discussion

Conclusion