Elsevier

Computers & Graphics

Volume 35, Issue 4, August 2011, Pages 878-884
Computers & Graphics

Cultural Heritage
Digital preservation and dissemination of ancient lithic technology with modern micro-CT

https://doi.org/10.1016/j.cag.2011.03.001Get rights and content

Abstract

Flaked stone tools were first made and used by early humans from at least 2.6 mya. By analysing temporal, geographical and species-specific variations in tool morphology scientists attempt to understand the evolution of cognition, culture and human behaviour. However, the dispersal of artefact collections around the globe in a large number of institutions makes direct study and comparison of the artefacts problematic, and therefore dependant on published drawings and photographs. The present study aims to determine whether CT could be used to create computerised (“virtual”) artefacts, and data shared with scientists and the public. In particular this study assesses whether CT would be cost effective and capture the fine surface topology created by the knapping process. Scanning could cost as little as €2 per flake. It was found that micro-CT could produce accurate high-resolution “virtual” artefacts that resolve features greater than 50 μm. Importantly, it was possible to visualise the key features of percussion, which distinguish intentionally made flakes from natural breakage. Furthermore, it was possible to recreate missing flakes (or parts thereof) from refitted groups of material by visualising void spaces. Hence it is possible to obtain a better understanding of the knapping process and obtain a glimpse of the flakes that were actually used as tools. The virtual flint artefacts are completely interactive and can be manipulated, viewed, measured and analysed as though they were in the hand and more useful to researchers than 2D drawings or photographs. The models are only 20 MB in size and can easily be distributed online, widening access to collections and access to physical specimens could be replaced with rapid stereotypes (3D prints). In addition, micro-CT imaging technology may give rise to new online “Virtual Museums” where digital data are shared widely and freely around the world, but the original material is conserved in mint condition, only to be removed for new or improved non-destructive imaging techniques.

Graphical abstract

“Virtual” online museums created using X-ray micro-CT will widen scientific and public access to valuable, rare and fragile cultural artefacts, such as ancient stone tools.

  1. Download : Download high-res image (39KB)
  2. Download : Download full-size image

Highlights

► Ancient flint stone tools are valuable for studying the evolution of human culture and cognition. ► Access to some museum collections is restricted because flint tools are rare and fragile. ► “Virtual” tools (including missing flakes from refits) can be created using micro-CT and rendered in three-dimensional perspective. ► “Virtual” tools are completely interactive and can be viewed and measured as though in the hand. ► Museums could widen scientific and public access to rare cultural artefacts.

Introduction

Lithic technology refers to a broad array of methods used to produce usable tools from various types of stone. Stone tools are commonly made from flint via the process of hard hammer percussion. A flint core is repeatedly struck with a harder stone to break off sharp flakes (Fig. 1). The flakes are often retouched to shape, sharpen or blunt the edges for improved function. Although some cultures still use stone tools today, most lithic technologies are associated with prehistoric societies or cultures and extinct species related to modern humans. Understanding how lithic technology was conceived and developed can help reveal when and how modern human cognition and culture evolved [1], [2], [3], [4]. Hence, museum collections of lithic artefacts have great historical, social and scientific significance. Flint is a rather stable, but somewhat brittle, material. Its handling and replication are likely to alter or remove microscopic use-traces and residues, which are critical for understanding how the tools were used, whereas the artefacts can potentially be damaged during their transport between institutions. Thus, it is difficult to compare collections stored at different institutions.

Artefacts have traditionally been illustrated with drawings [5] and/or photographs [6] alongside written descriptions. Drawings can be subjective and open to interpretation [7]. Photography is more objective, but it does not always show the key technological features of the artefact. Broadening the access to lithic collections would support the analysis of temporal, geographical and species-specific variations in morphology and technology. One way to accomplish this would be to create computerised “virtual” tools that could be shared, thereby widening the access while maintaining the safe-keeping of the original artefacts. A suitable virtual technique must be able to record the size and shape of a flint and, in particular, its surface topology. The cracks, fissures and ripples on the surface of a flake provide a record of the flaking process and can be used to determine whether a stone was intentionally modified by humans (i.e., an artefact) or created naturally (i.e., a geofact) [8]. The virtual technique must also be non-destructive [9] and non-contact. The resulting data set must be fully three-dimensional and should provide the means to manipulate, view and measure a virtual specimen as though it was held in the hands.

A number of techniques have been applied to record virtual data in cultural heritage contexts (see Table 1 for some examples) [10]. Almost all the listed techniques are non-destructive, except serial grinding [11], [12] and casting. Casting is likely to leave residues on the convoluted surfaces of an artefact and might also damage the flint when removing the specimen from the mould. Similarly, contact measurement with calipers or a micro-scribe may also damage artefacts. Drawing, microscopy and photography require little handling but do not produce fully three-dimensional (3D) data sets that can be manipulated on a computer. It is possible to visualise objects in 3D by generating stereo-anaglyphs or digital elevation models, but this can only be done for one surface at a time. The only systems capable of producing true 3D models of specimens are laser (stereo-) photogrammetry and volumetric scanners, such as magnetic resonance imaging (MRI) and computed tomography (CT). Laser scanners emit light and detect the reflections to map the surface of an object as a point cloud. Flint tools are not suited to this technique because the surfaces are reflective and translucent (see [13]). Reflective surfaces create noisy point clouds, and translucency causes subsurface scattering that degrades image quality, particularly near sharp edges. Photogrammetry refers to the use of two-dimensional (2D) photography for reconstructing computerised 3D surface maps [14] of substrates [15], buildings [16] or objects [17]. Taking a photograph projects 3D objects into 2D, and photogrammetry reverses this process. Flint is well suited to the technique, which can produce realistic colour by mapping the photos onto the 3D computerised reconstruction [18], [19], [20]. However, where cracks, fissures or flake scars infold the laser and photogrammetric instruments cannot penetrate the flint to create an image. Hence, convolutions create gaps in the reconstructed 3D surface and can preclude the effective scanning of some artefacts.

Furthermore, photogrammetric and laser techniques cannot record the internal features of a refitted group. Refitting is the process of reconstructing a flint block by replacing flakes onto the block in the order in which they were removed [21], [22]. Particular pieces may be missing from reconstructed blocks, and they may have been carried away from the location where knapping took place. With volumetric scanners, it should be possible to make 3D reconstructions of voids and thus create virtual models of missing pieces. While the most probable forms of the missing pieces can be loosely inferred from the shapes of any voids and the orientations of the flakes that preceded the missing material, it is impossible to be sure of the exact form of the missing pieces without modelling them. For instance, the orientation of preparatory flakes preceding a missing piece might suggest that methods had been deliberately employed to produce pointed forms. Modelling the missing flakes allows the determination of whether particular types of end product were intentionally produced and used or whether the attributes of the missing pieces were more variable. Such observations have implications for understanding the behavioural and cognitive nature of particular technological strategies.

The MRI technique, using magnets to image hydrogen content, is not suitable for dense stones because of their low water content. In contrast to laser, photogrammetric and MRI scanning, CT uses penetrating radiation to image an object and can therefore reconstruct objects that are reflective and translucent and have a convoluted infolding surface and a high density. To date, numerous studies have employed CT to image rocks, stones, fossils, bone and teeth [23], [24], [25], [26], [27].

Micro-CT is a powerful non-destructive imaging modality for the full-volume visualisation and inspection of an object in 3D [28], [29], [30]. The present study aimed to determine whether CT can be used to create “virtual” artefacts and whether the data can be used to provide wider access for scientists and the public. In particular, this study assesses (a) whether CT could capture the fine surface topology created by the knapping process and (b) if flakes missing from refits can be visualised. The findings are discussed within the wider context of museum preservation and research strategies.

Section snippets

Sample

The efficacy of CT for visualising flint artefacts was tested using a single flake and a refitting group of flakes. The single flake (Fig. 1a) was selected from a >0.78-million-year-old (mya) assemblage excavated at Happisburgh (Norfolk, UK). The assemblage comprises simple flakes, flake tools and cores, assigned to a ‘flake and core’ or Mode 1 technology. The earliest appearance of Mode 1 technology was the Oldowan Industry ≈2.6 mya in East Africa. By ≈1.7 mya, Mode 1 assemblages also existed in

Results and discussion

Stone artefacts provide valuable insight into the evolution of human behaviour and cognition [2]. Using CT scans to provide 3D rotatable models of stone tools opens the access to information about stone tool technology and typology and allows the critical assessment of the human or natural processes involved. Furthermore, CT scans can be an important research tool to investigate the nature of missing pieces from refitting groups.

The Happisburgh flake (Fig. 1a) has a proximal striking platform

Acknowledgements

The authors would like to thank the British Museum for funding the Happisburgh excavations. We would also like to thank the following people: C. Stockton and S. Stockton for their practical support; B. Farrow and P. Frew (North Norfolk District Council), E. Couzens, the Lomax family (local landowners) and M. Kerby (North Norfolk Coastal Concern Group) for permitting and facilitating the excavation; J. Roylance and M. Appleford for the plant hire and machining and Rob Kruszynski for arranging

References (74)

  • A.C. Jones et al.

    Imaging assessment of bone in growth into porous biomaterials using Micro-CT

    Biomaterials

    (2007)
  • J. Rant et al.

    Neutron radiography examination of objects belonging to the cultural heritage

    Appl Radiat Isot

    (2006)
  • F. Casali

    X-Ray and neutron digital radiography for cultural heritage

  • R.A. Ketcham et al.

    Acquisition, optimization and interpretation of X-ray computed tomographic imagery: applications to the geosciences

    Comput Geosci

    (2001)
  • R.L. Abel et al.

    Fluid flow in and around the olfactory organ of a hammerhead shark

    Comp Biochem Phys A

    (2010)
  • S.H. Ambrose

    Paleolithic technology and human evolution

    Science

    (2001)
  • R. Foley et al.

    On stony ground: lithic technology, human evolution, and the emergence of culture

    Evol Anthropol

    (2003)
  • N. Toth et al.

    Early stone industries and inferences regarding language and cognition

    Tools, language, and cognition in human evolution

    (1993)
  • S. Semaw et al.

    2.5-million-year-old stone tools from Gona, Ethiopia

    Nature

    (1997)
  • R. Aerts et al.

    The accumulation of Stone Age lithic artifacts in rock fragment mulches in northern Ethiopia

    Geoarchaeology

    (2010)
  • D.M. Lopes

    Drawing in a social science: lithic illustration

    Perspect Sci

    (2009)
  • J.C. Whittaker

    Flintknapping: making and understanding stone tools

    (1994)
  • C. Vilbrandt et al.

    Cultural heritage preservation using constructive shape modeling

    Comput Graph Forum

    (2004)
  • W.N. Croft

    A parallel grinding instrument for the investigation of fossils by serial sections

    J Paleontol

    (1950)
  • D.V. Ager

    Serial grinding techniques

  • G. Sansoni et al.

    State-of-the-art and applications of 3D imaging sensors in industry, cultural heritage, medicine, and criminal investigation

    Sensors

    (2009)
  • Z. Lina et al.

    Drainage density, slope angle, and relative basin position in Japanese bare lands from high-resolution DEMs

    Geomorphology

    (2004)
  • Guidi G, Beraldin JA, Ciofi S, Cioci A, Atzeni C. 3D acquisition of Donatello's Maddalena: protocols, good practices...
  • S.P. McPherron et al.

    Stone tool analysis using digitized images: lower and middle paleolithic

    Lithic Technol

    (1999)
  • T.A. Sumner et al.

    A virtual paleolithic: assays in photogrammetric three-dimensional artifact modelling

    Paleo Anthropol

    (2008)
  • B.P. Flannery et al.

    Three-dimensional X-ray microtomography

    Science

    (1987)
  • S. Ashkenazi et al.

    Fossil embryos and adult viviparids from the Early-Middle Pleistocene site of Gesher Benot Ya'aqov, and their ecology, longevity and fecundity

    Lethaia

    (2009)
  • R.J. Butler et al.

    A possible ctenosauriscid archosaur from the Middle Triassic Manda Beds of Tanzania

    J Vertebr Paleontol

    (2009)
  • G.R. Davis et al.

    X-ray microtomography of bones and teeth

    Physiol Meas

    (1996)
  • G.N. Hounsfield

    Computerised transverse axial scanning (tomography): part I. Description of system

    Br J Radiol

    (1973)
  • A.M. Cormack

    Representation of a function by its line integrals, with some radiological applications

    J Appl Phys

    (1963)
  • M.P. Morigi et al.

    Application of X-ray computed tomography to cultural heritage diagnostics

    Appl Phys A—Mater

    (2010)
  • Cited by (55)

    • Virtual micromorphology: The application of micro-CT scanning for the identification of termite mounds in archaeological sediments

      2019, Journal of Archaeological Science: Reports
      Citation Excerpt :

      Despite the recent use of micro-CT scanning in geoarchaeology, the technique has long proven its value in the earth sciences (see reviews in Carlson, 2006 and Cnudde and Boone, 2013). Micro-CT has been commonly used for the three-dimensional visualization of sedimentary components, in studies dealing with: the texture and porosity of sediments and rocks (Baker et al., 2012; Bendle et al., 2015; Carlson et al., 2000; Gualda and Rivers, 2006; Ketcham, 2005; Kilfeather and van der Meer, 2008; Landis et al., 2000; Tarplee et al., 2011; Voltolini et al., 2011); three-dimensional petrography (Van Geet et al., 2001); soil studies (see review in Taina et al., 2008); conservation of buildings (Cnudde et al., 2004; Rozenbaum, 2011); analyses of archaeological artifacts (lithics, ceramics, bone, ostrich eggshells, antler and wood objects) (Abel et al., 2011; Bello et al., 2013; Bugani et al., 2009; Haneca et al., 2012; Kahl and Ramminger, 2012; Mcbride and Mercer, 2012; Mizuno et al., 2010; Ngan-Tillard et al., 2016; Yang et al., 2018); plant remains in the archaeological context (Coubray et al., 2005); and midden composition (Adderley et al., 2001; Huisman et al., 2014; Ward and Maksimenko, 2019). In this study, we conducted the micro-CT scanning of impregnated blocks of sediment from the archaeological site of Lapa do Santo (Minas Gerais, East-Central Brazil) (Fig. 1) to investigate the presence of an intriguing component initially identified through micromorphological analyses – termite mound fragments described in the early Holocene levels (Villagran et al., 2017).

    View all citing articles on Scopus
    View full text