This research develops hydroxyapatite (HAP)- based, inorganic mineral systems with improved properties for the consolidation of powdery wall paintings of archaeological, historic and artistic value. The interdisciplinary nature of this research focused at the interface of archaeology, conservation science, biotechnology, and materials science, develops tailored 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 protective HAP crystals by triggering reactions between the carbonate-rich layers of wall paintings and ammonium phosphate precursors (Figures 1&2) based on the reaction: 10 CaCO (NH 4 ) 2 HPO 4  Ca 10 (PO 4 ) 6 (OH) 2 +10CO 2 ↑ +12NH 3 ↑ +8H 2 O. This consolidation treatment enables the protection of multi-layered, polychrome, heterogeneous wall paintings from weathering and deterioration induced by passage-of-time and environmental action linked effects. Figure 2: SEM micrographs showing the formation of hydroxyapatite (HAP) placed in contact with ammonium phosphate precursors (DAP and MAP respectively). Biomimetic methods based on soluble ammonium phosphate precursors for the consolidation of wall paintings Ioanna Kakoulli, University of California-Los Angeles, DMR DAP Solution Transport Japanese tissue (intermediate layer) Ca-rich block (sample) Cellulose pulp (poultice) soaked with DAP solution Figure 1: Schematic diagram (left) and photo (right) illustrating the application of ammonium phosphate precursors on test panels.

By the application of spatially-consistent and structurally and compositionally sensitive analytics including SEM-EDS, vapor sorption, 3D-CT imaging, mechanical and fluid-transport analyses, this research forwards approaches to prescribe/quantify HAP treatments to achieve a desired level of consolidation of porous structures (Figures 3&4). From a scientific perspective, the research develops information to relate: (1) the chemical interactions and kinetics of reactions between the phosphate reactant and plasters containing CaCO 3 at various pH levels to quantify the rate/extent of consolidation (HAP formation), (2) the impact of HAP formation within the decohesive layers in terms of microstructure- linked, fluid-transport, mechanical, durability and colorimetric properties and (3) the chemical interactions of the reactant precursors with different pigments and binding media (inorganic and organic) present in the substrate. 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 material. Figure 3: BSE micrograph (left) and EDS elemental maps of Ca and P showing newly formed calcium phosphate phases in areas originally occupied by the microcrystalline CaCO 3. Water absorption test was performed according to the modified version of the ASTM standard C1585 I = the absorption m t = the change in specimen mass in grams, at the time t a = the exposed area of the specimen, in mm 2 d = the density of the water in g/mm 3 Figure 4: Measured reduced water absorption for samples treated with DAP. Biomimetic methods based on soluble ammonium phosphate precursors for the consolidation of wall paintings Ioanna Kakoulli, University of California-Los Angeles, DMR

The interdisciplinary nature of this research involves professors from different backgrounds and departments including materials science and engineering, conservation, archaeology, civil engineering and bioengineering. The research and academic training provided to a post-doctoral researcher (Magdalena Balonis) two graduate students (Dian Yu and Xiao Ma) and undergraduate students (Nathan Wong, Zhaoying Yao, Nuoya Xie) imparts knowledge to a new generation of interdisciplinary scientists who can contribute to preserving our collective cultural heritage. Through interactions with national and international collaborators between academia and museums, this research offers a platform for academic excellence/exchange and at the same time creates new knowledge of conservation practices applicable across diverse geographical domains. The project further enhances the education and outreach efforts by attracting highly qualified students from underrepresented minorities and faculty to work on interdisciplinary research projects. The research also develops knowledge with applications in bioengineering for tooth/bone reconstruction, for infrastructure rehabilitation in civil engineering, as well as for the conservation of ancient bone, ivory and horn. Archaeological bone consolidation using HAP is currently under investigation through collaborative research with the UCLA /Getty Conservation Interdepartmental Program at UCLA. A blog/website for this project (Figure 6) was created and serves as an information resource for researchers and the general public. Archaeomaterials Group Hydroxyapatite (HAP) Project p-project/ Figure 6: HAP project website. Figure 5: Undergraduate students Nathan Wong and Zhaoying (Wendy) Yao preparing samples for analysis. Biomimetic methods based on soluble ammonium phosphate precursors for the consolidation of wall paintings Ioanna Kakoulli, University of California-Los Angeles, DMR