The Glass Collection of Ferdinand II in Museu Nacional de Arte Antiga: study and preservation

Abstract

Up to the present work, there was no systematic study on the glass collection gathered by King Ferdinand II of Portugal in his main residences (Palace of Necessidades and Palace of Pena) during his lifetime. This dissertation comprises the first comprehensive study on this glass collection and it aimed to contribute to the history, increase of artistic value as well as to the preservation of the precious objects nowadays mainly stored in Museu Nacional de Arte Antiga (MNAA). This is collection at international level, encompassing a wide range of glass objects from different European production centres within a wide chronology, thus becoming a fine case study. Despite the indisputable value of the glassworks selected and privately exhibited by Ferdinand II in the 19th century, its majority still remains out of public display. This thesis offers the first complete approach to the history, art historical contextualisation, material characterisation, assessment of conservative state and corrosion behaviour of the glass artefacts of this collection. These artefacts are representative of historic glass productions and, as other coeval collections, are the primary sources and the historical testimonies for the unfolding of glass history. The methodology adopted in this study had the main purpose of covering all the aforementioned areas intimately connected with the group of glass objects. Firstly, the result of the research from records, archive documents, collecting context, and the history of the collector himself resulted in the improvement of the comprehension of this group of objects, where exquisite pieces of luxury glass with internationally recognised production quality are represented. Secondly, the results from the chemical characterisation supported the wide variety of origins stylistically observed, at the same time allowing observations concerning the technology and the conservationstate of the materials. The conservative state of several objects imposed challenges to the glass conservation field. Numerous responses were found through the scientific approach to the surface glass corrosion. Three main conclusions could be drawn: (i) in soda-rich glasses the increase in RH is proportional to the increase of the thickness of the hydrated layer, and the composition influences the degree of deterioration observed for each glass type (Na2O increase and/or CaO decrease) (ii) in potassium-rich glasses, even with high-silica content matrices, the influence of small additions of PbO seems to be of great relevance for the reactivity of the surface with water (likely through a network disrupture, connected porosity and lower tendency to form a passivation layer), and (iii) in mixed-alkali formulations (especially in the presence of mixed-modifier cations and higher lime contents), the resistance to moisture attack is high and similar glassworks show a very good state of preservation even when exposed to less favourable conservative conditions. Based on sound physico-chemical principles, a few measures – such as endowed changes in RH in storage, case-specific for Cristallo-like compositions or high-soda content façon de Venise, as well as to Pb-containing K-rich glasses –, were proposed in order to preserve these relevant glassworks. Due to the fact that the replica materials were also representative of compositions found in many other museums’ collections, the conclusions draw from this study are of great importance to glass collections in similar conditions elswhere. Ultimately, this dissertation offers the basis of knowledge for the preservation and increase of value of this glass collection, and presents relevant results for other similar glass collections. Future work is necessary for the evaluation of the real effect of the proposed measures, along with their effective usage in situ.