Future of nanoindentation in archaeometry

This review aims to consolidate a scattered literature on the use of a modern nanomechanical testing techniques in archaeometry materials research such as the process of mummification. It is concluded that nanoindentation tests can provide valuable data about mechanical properties which, in turn, relate to the evolution of ancient biomaterials as well as human history and production methods. As an emerging novel application of an existing technique, some special considerations are warranted for characterization of archaeometry materials. In this review, potential research areas relating to how nanoindentation is expected to benefit and help improve existing practices in archaeometry are identified. These probe new insights into the field and will hopefully raise awareness for use of nanoindentation in world heritage sites.


INTRODUCTION
Inspection of archaeological materials (e.g. metals, paints, claws, teeth, stones, bones, skins, etc.) is often an intricate task due to fabrication history, the composite chemical and structural alterations that are caused by the alloying, annealing, and working processes of production, as well as by post-manufactured conditions. For centuries, archaeologists have been seeking to use analytical methods that can yield detailed quantitative and accurate interpretations about the prehistoric past. The analysis of archaeological objects necessitates investigators to address the problem, by knowing features like grain size (i.e. microstructure) and other measurable characteristics of the item. A natural question arises: Is it is possible to go backwards to obtain insight into the forming conditions or production processes? [1].
Therefore, the principle motivations and applications of nanomechanical testing (nanoindentation) to archaeological materials would be understanding ancient manufacturing, storage, and usage processes by characterization of microstructure, and doing the above within small test volumes in small, rare and/or potentially priceless samples. A potential for ageing studies exists also exists for the technique, however these remain much less developed to date. Nanoindentation (ISO 14577 [2] and ASTM E2546-07 [3]) is a technique with high spatial resolution to precisely characterize and probe the mechanical behaviour of materials [4]. The technique is applied widely in the areas of aerospace, energy, electronics, and healthcare, and deals with a range of materials like carbon fibre reinforced polymer (CFRP), carbon materials, coatings and alloys, civil engineering and polymeric materials, organic feedstock materials in bioenergy area and semiconductor materials like silicon to probe useful properties like hardness, modulus, fracture toughness, wear resistance, coefficient of friction, creep, visco-elasticity and interfacial bond strength. It has precedence in historical contexts as well, being used recently, for example, to analyse dental wear mechanics in Hadrosaurid dinosaur samples [5]. The importance of instrumented nanoindentation in the field of archaeometry stems from the fact that the microstructure and surface mechanical properties of materials can help archaeologists to determine the settings under which they were fabricated, used and stored. Studying and probing the process of mummification (shown in Fig. 1, indentation zone encircled) [6] dating back to 50 centuries ago is by far the best example of putting nanoindentation in practice.
An understanding of microstructure is a pathway to examine the methods and the degree of control available to ancient manufacturing processes. Further, the surface nature of nanoindentation can reveal clues about the contact history of samples otherwise invisible to macroscopic mechanical testing: Signatures of rubbing, scraping, crushing, cutting and other abrasive or reforming processes can be revealed in the mechanical signals. Exotic samples obtained from archaeological sites require minimally destructive testing methods. The data produced by nanoindentation complements data from other archaeometry methods; For example, the tandem use of multiple surface characterization techniques such as energy dispersive X-ray spectroscopy, electron backscatter diffraction, infra-red spectroscopy, optical imaging, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray fluorescence, etc. provides access to variables of archaeological material properties and performance that cannot be gathered from other analytical techniques or grain size analyses only. These supplementary characterization techniques provide a basis for interpreting nanoindentation results when they differ from one sample to the next by, for instance, establishing statistical correlations between elastic modulus and the underlying composition of a material. This is especially true when nanoindentation and a complimentary technique are collected at precisely matched sites.
Overall, the ability of the nanoindentation technique to quantitatively characterize the mechanical properties of individual microstructures, phases and constituents in bulk materials at the nanoscale has been critical for making revolutionary advances in materials characterization.
Archaeological samples are interesting sources of study for phenomena such as aging, alloying, carbon dating and other processing techniques from ancient human civilisation and are therefore of technological intellectual curiosity. New areas of research have traditionally been useful to push forward innovative methods in materials characterization; the test case of applying Raman Spectroscopy for characterization of graphene is an ideal example. One of the principle concerns for testing archaeological samples is preservation, placing a high value on minimally invasive or non-destructive techniques. The criterion for this includes not only structural integrity but also ensuring aesthetic quality for museum display etc. is not compromised. As a technique that probes sample volumes of a few cubic microns or less, well below unaided visual detection, nanoindentation offers a way to extract mechanical data while preserving specimens.
It is also the purpose of this review to show that this nanomechanical method can fill an important gap in experimental characterization of materials in archaeometry, whilst also using other methods to supplement the other aspects of this research field including the likes of techniques such as transmission electron and atomic force microscopy. Research in archaeometry incorporating nanoindentation methods has been scarce but appears to be increasing. Examples in metals [1,7-10], minerals [5,[11][12], enamels [13][14], claws [15], paints [16], bones [17][18], and skins [6] are now present in the literature. However, a consolidated understanding on the origins and future pathways of how the technique may be used for samples being extracted from precious world heritage archaeological sites as well as the range of existing materials available in museums worldwide is currently missing. This motivates our review, which attempts to demonstrate the uptake of the instrumented nanoindentation technique and its utility in advancing the archaeometry materials research.

INDENTATION CONTACT MECHANICS AND MEASUREMENTS
Instrumented indentation or nanoindentation consists of pressing a rigid (typically diamond) probe or indenter of well-known geometry into the surface of the material under investigation and assessing the ensuing deformation via a high-resolution measurement of displacement. Material mechanical properties are determined by analysing the forcedisplacement-time (P-h-t) plots recorded during indentation [19][20]. Instruments standardly supply sub-microNewton force and sub-nanometer displacement resolution with large dynamic range. On some occasions, microscopic examination of the impression "fingerprint" left by the indenter in the substrate is performed by optical or scanning probe microscopy upon its retraction. Nanoindenters are also available for in-situ SEM and TEM observation during mechanical testing.
Mechanics for elastic, visco-elastic, and elastic-plastic constitutive models have been proposed to describe indentation response (stress state and material accommodation) in variety of materials [21][22][23][24]. For material with elastic properties, the indentation impression vanishes after unloading cycle, whereas, for material with plastic properties, permanent deformation appears around the indentation. For elastic-plastic ductile materials like many metals, analytical slip-line field models estimate the permanent deformation along available slip-lines based on yield stress criterion (Tresca or von-Mises) [25], while complex materials require advanced constitutive models and numerical simulation. For plastic deformation in isotropic, ductile material, the standard indentation model [22,[25][26] assumes material accommodates the indenter volume by an outwardly expanding hydrostatic core. This hydrostatic core provides symmetry of the stress field under the indenter and which governs the development of concentric hemispherical plastic and elastic shells of deformation that surround the contact [27].
It is well known that the mechanical response of viscoelastic materials depends on load magnitude and contact duration, where the indenter continues penetrating the specimen even under constant load. Under standard analysis, these phenomena can lead to errors in the determination of contact depth which appears as a decrease in apparent elastic modulus and hardness with time [28]. The parameters in a model for viscoelastic response are usually determined from the time course of indenter penetration under constant load [28]. However, the displacement will also be influenced by the initial period of load-increase. This can be considered by correction factors.
It is important to note that the depth-sensing capability of modern instrumented indentation was initially combined [29][30] with traditional indentation methods [21] because of the difficulty at small scales to precisely measure the hardness impression projected contact area upon unloading [29]. However, it was soon realized that this capability allowed for a simple means to simultaneously extract the elastic properties of the material [4], which accounts for much of the wide popularity of the technique today. The basic nanoindentation test simultaneously measures both elastic modulus and hardness of small-volume samples.
For isotropic materials, the elastic modulus measured is a convolution of Poisson's ratio (ν) and elastic modulus (E), the latter of which is often extracted by assuming a value for the former (most structural materials lie in the 0.3 to 0.4 Poisson ratio regime). The hardness (H) is a semi-intrinsic material property associated with the plastic tensile yield strength (σ) of the material by the empirical Tabor relation (H=Cσ), where the confinement parameter C~3 for metals and ceramics and C~1.5 for glassy polymeric matter [29]. A variety of indentation features and response can also be measured by considering the deviation of forcedisplacement loading profiles with that of a reference specimen at the same indentation depth or load [30].
The physical quantities measured from the load-displacement (P-h) curve relevant for mechanical property and residual stress measurement are: the maximum load (Pmax), maximum indentation depth (hmax), contact depth (hc), final indentation depth (hf), contact area (Ac). The Oliver-Pharr model [4] is the most frequently used method to obtain various mechanical properties (e.g. hardness and elastic modulus) during nanoindentation.
Traditionally, the residual elastic modulus (Er) is derived by measuring the initial unloading contact stiffness (S) which is the slope of the first one-third linear part during unloading cycle of the P-h curve. We provide a few further key technical details here, for a complete description of nanoindentation procedures and theory (see e.g. [31][32][33][34][35]). The mean indentation contact pressure or hardness, H, is calculated as [4,33]: where, Pmax is the maximum indentation force, Ac is the contact area between the indenter and the surface of the material, which is a function of contact depth, hc, for example: for an ideal conical indenter, where α is half apex angle.
The contact depth is calculated as [4,33]: where ω is a geometric parameter (1 for a flat punch indenter, 0.75 for Berkovich rounded (4) where Ei, νi is elastic modulus and Poisson's ratio of the diamond tip. Reduced modulus Er is calculated from Sneddon equation [36]: Er = (√π/2).(S/√A), S = dP/dh (5) where A is the projected area of elastic contact, S is the contact stiffness. In modern instruments, one can also measure the stiffness continuously [37]. A recent advance in nanoindentation is called 4D tomography, whereby the substrate is mapped over its volume (to a certain depth) at a very high indentation speed [38].  [44].

Materials and surface preparation
Historically, flat surface preparation for nanoindentation of most of the engineering materials (e.g. metals, ceramics, coatings) has been commonly done through metallurgical precision cutting, mounting (cold/hot), grinding and fine polishing processes. Apart from metals, the exemplar specimens investigated using nanoindentation includes analysis of range of archaeological material types, e.g. teeth, stones, paints, claws, bones, skins, etc. As flatness is key assumption of most analysis techniques, surface preparation can have a marked influence on the repeatability of the nanoindentation measurements results of such precious archaeological materials. In this case other sample preparation techniques such as microtoming (cutting extremely thin slices of material) and cryo-microtoming developed for microscopy can be valuable. In all cases careful validation of sample flatness by optical, electron, scanned probe or other high-resolution microscopies is critical.
However, one may note that the variation in nanoindentation measurement is particularly true for biological tissue specimens due to the effort of sample fixation. It is also known both for compact and trabecular bone, that hardness and elastic modulus are dependent on the water content. These conditions result in up to 40% difference in measured indentation modulus [39,42].  [14], each of the molars inspected was tested on the buccal face, the occlusal tips, and in buccal-to-lingual cross-section taken midway between the tip and the gum-line. All test surfaces were prepared using the process (i.e. metallographically, samples were fixed to a lapping stub using polymer and then polished using a lapping fixture with sequentially finer alumina lapping films). Since nanoindentation testing are time-consuming process, in normal practice, the samples are tested in dry conditions to evaluate the properties of biological materials (e.g. bones, skins). Moisture promotes enzymatic deprivation of such biological materials (e.g. bones, skins), the bone collagen matrix and because the nanomechanical tests with large set of different test constraints take longer times, it would be very tough to preserve or sustain the test conditions during the experiments. For all these reasons, biological specimens to be tested are normally dried in stable conditions prior to the experiments, as it has been revealed through numerous investigations that the stiffness is generally complex (higher) than stiffness of the bone samples tested under wet conditions [39,42].
In an example of sample preparation for indentation of skin, Janko et al. (2010) [6] obtained histological specimens and 2 µm to 4 µm thick transverse (crosswise) sections were cut and transferred onto transparent slides. To prepare the histological sections, new skin samples were exposed to the same procedures as the mummified tissue. As a reference, Janko  [46] where the samples were mounted on the AFM and the nanoindenter sample pucks with a rapid drying glue, a method which is generally not implemented across all material types. In a work by Crichton et al. (2013) [47], the skin sample was mounted onto a stainless-steel stage with double-sided tape, and filter paper soaked in saline was placed in contact with the excision surface to ensure that the tissue did not dehydrate (possibly to maintain structural integrity of sample to an extent) from these surfaces during experimentation.

Metals
The extant literature provides examples of ancient metals that have been analysed using nanoindentation techniques. Changes within the structure of the metal could be identified which would identify microstructurally age-related modifications, to help determine the tempering processes involved, type of original material used and the composition of the metal [7,9]. For example, nanoindentation investigation has been done by whereas the indentation on matrix showed lower bound hardness (2.5 GPa) and significant hysteresis resembling a phase transition ( Fig. 3(a)). GPa, respectively (these data were higher than the hardness 2.78 GPa of the simulated as-cast

As shown in
Cu-24 wt.% Sn alloy). The results suggested that the vessels were probably made-up using the protocol: (1) alloying the high-tin Cu-Sn bronze; (2) casting the shape of the vessels; (3) forging the vessels at appropriate high temperature; (4) wiping tinning on the surface of the vessel at high temperature; (5) quenching the vessels to room temperature; and (6) grinding or polishing the surface of the vessels. They also suggested that the thin-walled bronze vessels provided an indication of the spread of thin-walled high-tin bronze technology in China.
Based on above investigations in metals of archaeological importance, it can be concluded that nanoindentation technique can be used to identify microstructurally agerelated modifications. However, further work to estimate other properties of materials can be understood based on improved understanding of the nanoindentation [19], possibly leading to clear differentiation between the respective contributions of manufacture, age and environment. It is also expected that the application of nanoindentation technique to archaeological metal specimens will enable characterization of crystalline phases existing within the alloy (e.g. Ag-Cu alloys, Fe3C, Cu alloys, bronze, etc, mentioned above) to develop empirical models of materials by incorporating properties of different phases, to obtain further insight into the forming conditions or production processes in the past.

Stones
The zircon stone contains trace levels of the radioactive elements Uranium (U) and Thorium (Th) that over the long period can cause some regions in the specimen to transform from crystalline to amorphous during the radioactive decay process. Oliver and Pharr (2010) [20] investigated a 570 million-year-old zircon stone (a layered structure) found in Sri Lanka (shown in Fig. 6(a)) using nanoindentation method, to study the radiation damage involving high-dose and short-term experiments. The sample slice taken was 30 µm thick, with radioactive trace levels of uranium (U) and thorium (Th) incorporated into the crystal. It was observed that the level of such radioactive elements resulted in a radiation dose very near that required to trigger an amorphization process in such materials. Some of the layers (not cracked ones) were completely amorphous, but the cracked regions were still crystalline.
Their suggestion was that the cracks appear because the amorphization process involves about a 17% decrease in density, so its expansion causes the adjacent crystalline material to crack. Oliver and Pharr (2010) [20] were interested in analysing whether the relationship between the long-term radiation dose level and the mechanical properties is the same as they see in short-term, high-dose experiments. indicates that the wear behaviour is influenced by the variation in contact stress fields during indentation cycle (loading, holding, unloading) caused by the microstructural transformations, changes in the residual stress fields and influence of grain size [19]. Based on above limited investigations in stones related materials, it can be concluded that nanoindentation technique can be used to develop empirical wear models, leading to correlation between the mechanical properties of the material and age-related modifications.
It is also expected that indentation technique can be used to quantify the fracture toughness of brittle stone materials, to obtain insight into the fragility of materials, which may assist in planning appropriate preservation or handling of such materials.

Enamels
It has been hypothesized that wear of enamel is sensitive to the presence of sharp particulates in oral fluids and masticated foods, and in the animal kingdom, wear can occur to an extent depending on the food source [49]. Surface observations of worn surfaces can reveal insight into wear micro-mechanisms, but are often obscured by debris and surface smearing, so that interpretations remain controversial [50]. Prediction of wear rates for different tooth forms under certain chewing conditions is of interest to evolutionary biologists. A principal concern is how wear rate is influenced by diet [51]. Therefore, Sanson The nanohardness results indicates that silica phytoliths (considerably softer) do not contribute as much to mammalian dental (harder) microwear as earlier reported and that exogenous grit and dust are a more likely cause. They also suggested that this premise could have implications for understandings of the causal agents of microwear phenomena in areas such as the evolution of high-crowned teeth in grazing mammals during the Miocene.

Riede and Wheeler (2009) [14] investigated middle-range link between the Laacher
See eruption and Late Glacial fauna and foragers: tephra (or rock fragments ejected during volcanic eruption) as dental abrasive and used nanoindentation to investigate tephra from several sites covering the medial and distal fall-out zones as well as the dental enamel of Homo sapiens and key prey species of Late Glacial foragers. As observed (Fig. 7), can be assumed to be time integral of several elasto-plastic micro-asperity events, they discovered the wear rate to be in strong correlation with Archard‫׳‬s law, which is a model used to describe sliding wear based on the theory of asperity contact [49]. Based on above limited investigations in enamel related materials, it can be concluded that nanoindentation technique can be used to develop empirical wear models, leading to development of mechanical properties correlation.

Claws
Claws reflects the natural history (e.g. feeding habits or locomotion) of mammals and birds. The claw geometry correlates well with arboreal and terrestrial habitats. It is likely that claws microstructure and mechanical properties would change over time, and properties of these types of materials would not always reflect their original functions. Dromaeosaurid theropod claws samples, such as Velociraptor (one of the dinosaur genera, Fig. 8(a) used nanoindentation method while investigating the mechanical properties of the keratin layer and cortical bone of the eagle owl claw (Fig. 8(b)). However, it is important to note that reliable indentation properties could not be obtained for such bones due to its highly porosity.

Paints
Ancient painting can be partly related with exerting influence upon expressions relied primarily on depiction subjects. Different layers of paint materials can be investigated using nanomechanical testing procedure, primarily for compositional analysis and understanding the aging process. There are very few literatures related to the application of nanoindentation technique to investigate mechanical properties of ancient paints.
In an example on ancient paints, Salvant et al. (2011) [16] investigated nanoindentation properties (shown in Fig. 9) which can be important for conservation and restoration purpose. One approach was to measure the mechanical properties of reconstructed paints: though, the aging process was poorly known, so it was also desirable to measure micromechanical properties directly on ancient paint specimens. Salvant  properties can be correlated to scratch resistance [52]. However, such correlation can be difficult to establish in pigmented paint coatings as dislodgement of pigments during scratch tests can lead to accelerated wear. Therefore, localised nanoindentation testing can yield information on paint properties without causing the dislodgement of pigments, however, time dependent indentation response (creep), leading to steeper and even negative unloading slopes and hence inaccurate mechanical properties [53].

Bones
Bone is a heterogeneous material containing three main phases: mineral, collagen, and water, arranged in a series of hierarchical structures [40]. Collagen contributes to bone's elastic and viscoelastic behavior while mineral stiffens the overall material, whereas, water contribute to elasticity and ductility. In modern times, scientific study of structure of bones is called as Osteology. Various factors such as age, death, sex, growth and development can be analysed with the identification of bone or its remains. Nanoindentation technique can be applied on bone skeletal remains to investigate mechanical properties to reconstruct the past, understand human variation, and provide information about the deceased individuals, or potentially identifying some pathological (study of disease) conditions.  [55]. It is even conceivable to measure direction dependent properties of structures using the nanoindentation method [55][56].
Although a general clinical practice is to perform the dual energy X-ray absorptiometry (DEXA) scan to measure the bone mineral density (BMD), changes in bone structures with age for both male and female can also be quantified using nanoindentation system [57].
However, in archaeometry the emphasis is to recover sample history details from the nanoindentation data which makes it more challenging. Following an organism's demise,  [18], with the geological age of the samples, a relatively small increase was seen in fossil bone specimens older than the Miocene, signifying that mineral infilling is limited by spatial saturation. An increased crystallinity and density correlated with an increase in elastic modulus, which shows a link between the crystal microstructure and the mechanical properties of samples.

Skins
Skin is the soft part of outer tissue which has three layers (epidermis, dermis and hypodermis), which protects us from microbes, helps regulate body temperature and permits the sensations of touch, heat and cold. The mechanical properties of skin are an important characteristic of its resistance to damage and important indicators of pathological situations [46]. There are very few literatures related to application of nanoindentation technique to investigate mechanical properties of ancient mummified skins (e.g. Fig. 1). mined samples from the Neolithic glacier mummy known as 'the Iceman'. When reference samples analysed from a volunteer of a similar biological age as the Iceman, microscopy using AFM exposed collagen fibrils that had characteristic banding patterns of 69±5 nm periodicity, i.e. sheet-like structures, and it is also characteristic for modern skin collagen [6].

Influence of external factors
It was observed that microstructure of dermal collagen bundles and fibrils were largely unaltered and very well conserved by the natural conservation process. Raman spectra of the ancient collagen showed that there were no substantial alterations in the molecular structure.
However, AFM based nanoindentation tests showed some changes in the mechanical behaviour of the fibrils. Elastic modulus of single mummified fibrils was 4.1±1.1 GPa, whereas, the elasticity of recent collagen averages 3.2±1 GPa. The preservation of the collagen after 5300 years indicated that dehydration owing to freeze-drying of the collagen is the main process in mummification and that the effect of the degradation can be potentially addressed. It is important to note that temperature variations, ultraviolet irradiation and the actions of insects, bacteria and fungi can potentially cause degradation, causing further skin tissue decay [6]. Based on above limited investigations in mummified skin, it can be concluded that nanoindentation technique using elastic modulus values can be used to develop correlation between the mechanical properties of the mummified fibrils and agerelated modifications, i.e. it resilience or durability.

CONCLUDING REMAKRS
This review argues that archaeology could substantially benefit from the use of the minimally-invasive nanoindentation techniques (as demonstrated in Fig. 11). The technique can help identify the material composition of artefacts, shed light into their construction, and characterize the mechanical properties of ancient tissues and biological constituents [58].
This can allow inference of, inter alia, local customs, range of habitation, trade patterns, and advancement of technology and development.
Bone, including dental material, is also an area where nanomechanical characterization techniques are frequently used, mostly on modern materials, but occasionally on ancient or fossilized artefacts. Abrasions as well as wear and stress patterns can provide useful information to the archaeologist, informing theories on human migration and habitation patterns [14]. Analysis of dinosaur claws can provide insight into strength and therefore postulate the way the claws were used and thus shed light on the habits of the dinosaur [15]. As bone and teeth are formed by minerals, local conditions will dictate the composition of the material and thus allow for a correlation between the sample, its origin, and its location [18]. Further, when applied to fossilised material, the results of the analysis can help identify the age of the material [17].
The nano-scratch technique was also used on modern and ancient steel to establish values of nanohardness and elasticity [8]. The scratch testing is of importance to access the fracture data of the unique range of exotic materials described above. These testing methods are also useful to access the values of friction coefficient which are now aiding to device the bio-inspired strategy to combat catastrophic damages [59]. Additionally, another example of understanding the bio-inspired designs (BID) can be seen in a range of studies varying from designing cutting tools for machining [60], transportation solutions [61], nanotechnology and so on [62]. By analysing the materials in bronze vessels to determine regional variations and shed light on the composition of the alloy and of the specific forging techniques used, information is obtained on the origin and spread of the technology [10] and of human migration and trade patterns. Indeed, the results of the analysis are crucial to understanding the relationship between environment and adaptation and evolution [63].
Potentially, the instrumented indentation technique can be used to quantify the residual stresses of materials [19,64] we anticipate a growing capability of mechanical parameters as measured by nanoindentation to be interpreted in terms of not only usage but also ageing states of various materials. This could be through specific radiation damage mechanisms as discussed in the review but may eventually encompass precision measurement of parameters affected by physical ageing of non-equilibrium phases.
Aging is a time-dependent process [67] and one of the important aspects in archaeometry. Aging (in the current context, for example, due to low or high temperature exposure, mechanical loading, radiation exposure, actions of insects, bacteria and fungi, tribological wear, etc.) can be explained as partial or total loss of their capacity to achieve the purpose, can lead to change in structural properties, and may impact the ability to withstand various challenges from operation, environment and natural events [67]. Except few examples, such as ultraviolet irradiation and the actions of insects, bacteria and fungi related degradation in skin [6], age-related variations at grain boundaries in metals [7], tribological wear of enamels [13][14], mechanical (ductility) properties for paint like materials [16], radiation related damage in stones [20], aging related characterization of archaeological This is an area which can provide further reliability on the application of nanoindentation technique. It also requires further investigation to bring out improvements to make this technique more satisfactory, as many interpretation issues in nanoindentation tests such as anomalies between loading-holding-unloading stages and occurrence of deformation and/or cracking are still unresolved. However, the trends reported in this review on the application of nanoindentation technique of archaeological materials show potential for its wider applications at world heritage sites. Also, a simpler user interface could also serve to build a strong case for how nanoindentation instrument could be useful as a routine tool to evaluate ancient materials properties.