Bridging silica and archaeology
Archaeology is a science based on the ability to retrieve embedded information from the archaeological records to reconstruct past events be they cultural or anthropological. Silicates are ubiquitous materials in archaeological sites. Precolonical ceramics are commonly found in South America, particularly, along the Amazon River and report back to approximately 5000 years ago. There is a huge archaeological record and an extensive anthropological interest in retrieving embedded information from the ceramics. One of the open questions posed by archaeologists, anthropologists and material scientist is: “How these ceramics were built considering their large size and material’s low mechanical properties?”
Recently, we have contributed to understanding the role of siliceous spicules as biological South America ceramic reinforcement component. The siliceous spicules, when embedded in the clay matrix, improve clay’s mechanical properties in terms of toughness and improve fracture propagation arrest.
F. Natalio, et al. ”Siliceous spicules enhance fracture-resistance and stiffness of pre-colonial Amazonian ceramics”, Sci. Rep., 5, 13303, 2015
Amazonian expedition 2014: aerial view
Schematic representation of the ancient Amazonian coil-roll technique used to orient the siliceous spicules (Demospongiae) to enhance the mechanical properties of pottery (e.g. utilitarian’s, cultural expression items).
Preserving ancient ceramic fabrication tradition
(a) Digital image of representative ancient pre-colonial Amazonian potsherd (vase wall, Santa Helena archeological site, N1049 E880, Brazil). (b) Low magnification optical microscopy image showing the presence of glassy structures attributed to siliceous spicules of the freshwater tree sponge Demospongiae Drulia uruguayensis (cauíxi). (c) SEM inspection of the same potsherd showing rod-like structures inside the clay matrix and displaying a preferential orientation. (d) Cross-section in the phase contrast-enhanced μ-tomography 3D data reveals co-alignment of spicules in different regions within the intact bulk of the sample. (e) Averaged image from (d). In both cases the spicules show preferential orientation. (f) SEM image of potsherd showing spicule alignment within the ceramic matrix.
In collaboration with:
Museu Paraense Emílio Goeldi (MPEG)
(a) Digital camera image of a standardized clay rod (10 × 4 mm) after heat treatment (500 °C for 1 h). (b) Scanning Electron Microscope (SEM) of clay rods containing siliceous spicules (5% wt) fabricated by the coil-roll technique (left image) and kneaded (right image) show a clear orientation and random distribution of the spicules, respectively. (c), i, Mechanical behavior of clay rods with randomly distributed spicules (5% wt). ii, SEM inspection after structural failure shows that spicules do not prevent crack propagation. (d) i, Mechanical behavior of clay rods with highly orientated spicules (5% wt). ii, similar behavior as for potsherds after structural failure, i.e., the crack propagates by surrounding the aligned spicules. The spicules remain structurally undamaged. (e) Schematic representation of the role of siliceous spicules in preventing crack propagation. (f) Schematic representation of the ancient Amazonian coil-roll technique used to orient the siliceous spicules (Demospongiae) to enhance the mechanical properties of pottery (e.g. utilitarian’s, cultural expression items).