Scientific Research

There are a few directions that are currenlty under way:

1. Research Project A (2012-present):In situ Synthesis and Characterizations of Bio-ceramic Based Hydroxyapatite in the Re-mineralization of Calcium-rich Matrices:

The research develops hydroxyapatite (HAP) based, inorganic mineral system with improved properties for the consolidation – providing the binding mechanism to reestablish the loss of cohesion – of powdery porous building materials (calcareous stone, marble, cement) and decorated architectural surfaces (rock-art, wall paintings and mosaics) of archaeological, historic and artistic value. The interdisciplinary nature of this research focused at the interface of materials science, biotechnology and conservation science develops tailored sustainable conservation treatments, which consider fundamental aspects of substrate chemistry and structure to prescribe and metricate treatment protocols. The scientific approach exploits biomimetic principles to induce the formation of HAP crystals by triggering reactions between the Ca-rich substrates of wall paintings and ammonium phosphate precursors such as diammonium hydrogen phosphate (DAP, (NH₄)₂HPO₄), and ammonium dihydrogen also known as monoammonium dihydrogen phosphate (MAP, NH₄H₂PO₄).

From a purely scientific perspective, the research develops new information to relate: (1) the chemical interactions, thermodynamics and kinetics of reactions between the phosphate reactants and CaCO₃, the main component in the stone, plaster or mortar, at various pH levels to the formation of orthophosphates such as HAP and rate/extent of consolidation (2) the impact of HAP formation within the decohesive layers in terms of microstructure-linked, fluid-transport, mechanical, durability and optical properties and (3) the chemical interactions of the reactant precursors with different pigments present in the surface paint layers. Acquired data show the potential of this treatment for the consolidation of powdery calcium carbonate-based surfaces and their protection from weathering and deterioration induced by passage-of-time and environmental action linked effects. These efforts develop quantitative materials science-based structure/property relations to engineer practical, prescriptive consolidation solutions in relation to the reactant chemistry, the substrate properties and the treatment application method relevant to the materials.

Figure shows the application of ammnium phosphate to do the evaluation of hydroxyapatite effects for the consolidation of a Hellenistic-Roman rock-cut chamber tomb at Athienou-Malloura in Cyprus

My group have carried out research work in the consolidation of excavated deteriorated ivories from Sanxingdui site.  The ivories, unearthed from the Sanxingdui site, have been buried underground for thousands of years. Over time, the organic matter within them has decomposed, and a substantial amount of clay has permeated, leaving the ivory relics fragile and severely deteriorated. Traditional consolidants, such as resins, are no longer sufficient to meet the conservation requirements. Hence, there is an urgent need to explore innovative materials for safeguarding these invaluable cultural heritage objects.  

We have employed a range of analytical techniques to gain insights into the phase composition, microstructure, and the deterioration mechanism of the waterlogged ivory. Building upon this knowledge, we have implemented novel materials and methods for consolidation. A three-dimensional networked structure of hydroxyapatite can be synthesized in-situ within the ivory, resulting in a consolidation effect. This treatment has significantly enhanced the mechanical properties of the ivory samples.

Selected Publications:

1. Xiao Ma* (corresponding author), Magdalena Balonis, Hélène Pasco, Michael Toumazou, Derek Counts, Ioanna Kakoulli, “Evaluation of hydroxyapatite effects for the consolidation of a Hellenistic-Roman rock-cut chamber tomb at Athienou-Malloura in Cyprus”, Construction and Building Materials, 150 (2017), 333-344.

2. Xiao Ma* (corresponding author), Hélène Pasco, Magdalena Balonis, Ioanna Kakoulli, “Investigation of the Optical, Physical, and Chemical Interactions between Diammonium Hydrogen Phosphate (DAP) and Pigments”, Sustainability 11 (2019), 3803.

3. Magdalena Balonis, Xiao Ma, Ioanna Kakoulli, “Phase relations in the system calcium carbonate/ammonium phosphate under aqueous conditions and 25°C”, Journal of the American Ceramic Society 103 (2020), 3837-3850.

4. Chao Wang, Siyi Xue, Yufeng Huang, Yangyang Li, Xiao Ma*(corresponding author), “Synthesis, characterization, and biological evaluation of “Bamboo lamellar” biomimetic hydroxyapatite”, Accepted, Ceramics International. DOI: 10.1016/j.ceramint.2025.01.285.

More Publications are currently under way…

 

2.Research Project B (2015-present): Archaeological building materials: characterizations

Given the significance of the site and the necessity in conservation intervention of the Ancient Buildings, a comprehensive multi-analytical study of will be undertaken, aiming to provide important information on the building construction technology taking into consideration several important parameters: 1) availability of geological resources providing the raw materials for the construction; 2) large facilities for the preparation of the building materials; 3) mechanisms of transportation and 4) technological knowledge.

We have studied archaeological materials from various locations, including several UNESCO world heritage sites, such as Wudang Mountains, Palace Museum, Great Wall, etc. 

Selected Publications:

1. Xuan Wu, Cui Jin, Mengjun Jia, Biao Cui, Celestino Grifa, Jixin Wang, Xiao Ma* (corresponding author),” An analytical study of the tabia mortar from Lin Yimu’s tomb, Zhejiang, China”, Heritage Science 12(2024) 351. 

2. Mengjun Jia, Guofeng Wei, Celestino Grifa, Jianhui Zhang, Biao Cui, Min Li, Jun Xu, Xiao Ma* (corresponding author), “Characterization of archaeological lime mortars in a Ming Dynasty tomb: a multi-analytical approach”, Archaeometry 65 (2023) 736-753.

3. Guofeng Wei, Chiara Germinario, Celestino Grifa, Xiao Ma* (corresponding author), “Characterization of ancient building lime mortars of Anhui Province, China: a multi-analytical approach”, Archaeometry 62 (2020) 888-903.

4. Li Xu, Xiao Ma, Bingjian Zhang, Qiong Zhang, Peng Zhao, “Multi-analytical studies of the lime mortars from the Yanxi Hall in Yangxin Palace of the Palace Museum (Beijing)”, Archaeometry 61 (2019) 309-326.

5. Xiao Ma, Guofeng Wei, Celestino Grifa, Yuhu Kang, Herant Khanjian, Ioanna Kakoulli, “Multi-analytical studies of archaeological Chinese earthen plasters: The inner wall of the Longhu Hall (Yuzhen Palace, Ancient Building Complex, Wudang Mountains, China)”, Archaeometry 60 (2018), 1-18.

 

3.Research Project C (2017-2022): Degradation mechanism of pigments in paintings

Oil paint is a heterogeneous mixture of pigments with a drying oil that contains a high degree of unsaturated fatty acid chains, and a variety of possible additives. Since the late 1990s, metal soaps have been systematically detected in oil paintings and could be linked to their deterioration, by causing brittleness, increasing transparency, or forming crusts on the paint surface, and even delamination leading to detrimental effects to the structural integrity and appearance of oil paintings.

The reaction between metal ions (from metal-containing pigments or modifiers) and hydrolyzed long-chain fatty acids (from an oil binding medium, such as linseed oil, poppyseed oil, walnut oil, etc.) leads to the formation of metal soaps. Among the metal soaps that may be formed, the research into zinc soaps and lead soaps has received most attention. Understanding the mechanism and rate of formation of metal soaps is essential to study the initiation factors and subsequent changes that lead to degradation of the oil paint and to plan preservation and conservation treatments. Two main questions need be answered:

1. How the soap formation initiated and what are the mechanisms and rates of soap formation within oil paints?

2. Can a protocol be established for the chemical and physical characterization of the metal soaps within oil paintings, particularly their morphology, crystal structure, and thermal and luminescent behavior?

This project aims to advance the research into oil paints aging in two ways: 1. to reproduce the chemical processes of the metal soap formation using models, via reaction between metal acetates and unsaturated fatty acid esters; 2. to improve the characterization of the metal soaps formed within both model systems and historical oil paintings.

Selected publications:

1. Xiao Ma, Georges Pavlidis, Eoghan Dillon, Victoria Beltran, Jeffrey Schwartz , Mathieu Thoury, Ferenc Borondics, Christophe Sandt, Kevin Kjoller, Barbara H. Berrie and Andrea Centrone, “Micro to nano: multiscale IR analyses reveal zinc soap heterogeneity in a 19th century painting by Corot”, Analytical Chemistry 94 (2022) 3103-3110.

2. Xiao Ma, Georges Pavlidis, Eoghan Dillon, Kevin Kjoller, Barbara Berrie, Andrea Centrone, “Nanoscale IR spectroscopy: from principles to nanoscale imaging and identification of metal soaps”, Microscopy and Microanalysis 27(S1) (2021): 2814-2815.

3. Xiao Ma, Victoria Beltran, Georg Ramer, Georges Pavlidis, Dilworth Y. Parkinson, Mathieu Thoury, Tyler Meldrum, Andrea Centrone, Barbara H. Berrie, “Revealing the distribution of metal carboxylates in oil paint from the micro- to nanoscale”, Angewandte Chemie International Edition 58 (2019), 11652-11656.