Dries Cnuts

Alterations caused by post-depositional processes have long hampered functional analysis of stone tools, and several attempts have been made to understand their effect on the visibility and identification of use-related traces and residues. Alterations can be caused by a broad range of phenomena that involve both mechanical and chemical processes. In this article, we present the results of an experimental study focused on the reproduction of alterations caused by repeated freeze-thaw cycles, which are among the crucial processes that many prehistoric artefacts have been subjected to after their deposition. Thanks to the use of a climate chamber, we succeeded in reproducing alteration polish comparable to what is frequently observed on prehistoric stone tools, in particular those dating to the Palaeolithic and Mesolithic periods. The results open new possibilities for exploring the effect of post-depositional processes on the preservation of use traces and residues, and demonstrate that alterations can also contribute to the understanding of site formation processes.

Understanding hunting technology is pivotal in the study of adaptive and innovative forces that influenced the evolution of prehistoric societies. The manufacture, design and use of hunting weapons involve technical processes such as those of tool miniaturization, blank standardization and projection modes, but also influence broader demographic structures such as human subsistence strategies, territorial organization and socio-economic structures. Here we present a unique discovery from a newly discovered site at Les Prés de Laure (Var, France). Excavations revealed a multi-stratified open-air site with archaeological units that were rapidly buried by the alluvium of the Jabron River. In a Gravettian layer dated between 25 and 23.5 ka cal BP, within an area apparently dedicated to horse carcasses processing and consumption, 11 backed points were discovered in direct association with altered bone remains. Wear and residue analysis of the lithic backed points in combination with complementary experimental data converge to indicate that the find represents a bone point armed with lithic barbs and used as hunting weapon. This discovery provides new evidence for the manufacture and use of hunting weaponry in a Gravettian context and stimulates discussion on Paleolithic weapon function and design, offering a unique window into the characterization of prehistoric hunting strategies.

The use of fire is essential for the preparation of hafting adhesives; both are suggested to be a proxy for distinguishing the technological expertise and complex cognition among Palaeolithic populations. While use of fire has been argued to exist from about 1.0 Ma onwards, evidence for adhesives in the Palaeolithic record is rare and fragmented. In spite of the close link between fire places and adhesives, no study has ever focussed on examining the impact of heat on adhesive deposition and preservation. This paper discusses the results of a combustion experiment that was undertaken to understand the impact of heat exposure on hafting adhesives. The results have significant implications for archaeological interpretations. Deposition in or near a fire proves to severely impact the types of residues that preserve on a stone tool. The vertically transferred heat is responsible for the loss of adhesives but also for the incidental production of adhesives and their deposition on stone tools. It can be hypothesised that the rare survival of adhesives on archaeological stone tools might not only be the result of direct contact with the fire but also the result of degradation due to heat from overlying fireplaces. If we are to improve our understanding of the preservation of adhesives, it is important to unstand the taphonomic processes that affect these adhesives, in particular heat alteration.

The identification of residues is traditionally based on the distinctive morphologies of the residue fragments by means of light microscopy. Most residue fragments are amorphous , in the sense that they lack distinguishing shapes or easily visible structures under reflected light microscopy. Amorphous residues can only be identified by using transmitted light microscopy, which requires the extraction of residues from the tool's surface. Residues are usually extracted with a pipette or an ultrasonic bath in combination with distilled water. However, a number of researchers avoid residue extraction because it is unclear whether current extraction techniques are representative for the use-related residue that adheres to a flaked stone tool. In this paper, we aim at resolving these methodological uncertainties by critically evaluating current extraction methodologies. Attention is focused on the variation in residue types, their causes of deposition and their adhesion and on the most successful technique for extracting a range of residue types from the stone tool surface. Based on an experimental reference sample in flint, we argue that a step-wise extraction protocol is most successful in providing representative residue extractions and in preventing damage, destruction or loss of residue.

Blind tests provide an objective means to evaluate the accuracy of functional interpretations based on the presence of use-wear and residue traces on stone tools. Previous blind tests have highlighted interpretive errors commonly associated with use-wear and residue analyses leading to significant methodological developments in each of the respective fields. While a number of blind tests have been performed on flaked stone tools, only a single blind test has been published for use-wear on grinding tools. We present the results of a two-part blind test performed on 15 experimental grinding implements that were used in a controlled setting, designed to evaluate the relative importance of residue analysis for determining the worked material (1) when contextual information is available and (2) when contextual information is absent. We argue that use-wear and residue analyses are successful procedures to identify the use of grinding stones, and that residue analysis may be a particularly valuable means for determining the worked material on tools that have insufficient use-wear development. We suggest that residues should be sufficiently abundant to infer use, if we are to avoid the potential confusion caused by contamination.

Headspace solid-phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) have traditionally been used, in combination with other analyses, for the chemical characterization of organic residues recovered from archaeological specimens. Recently in many life science fields, comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GCˆGC-TOFMS) has provided numerous benefits over GC-MS. This study represents the first use of HS-SPME-GCˆGC-TOFMS to characterize specimens from an experimental modern reference collection. Solvent extractions and direct analyses were performed on materials such as ivory, bone, antlers, animal tissue, human tissue, sediment, and resin. Thicker film column sets were preferred due to reduced column overloading. The samples analyzed by HS-SPME directly on a specimen appeared to give unique signatures and generally produced a higher response than for the solvent-extracted residues. A non-destructive screening approach of specimens may, therefore, be possible. Resin and beeswax mixtures prepared by heating for different lengths of time appeared to provide distinctly different volatile signatures, suggesting that GCˆGC-TOFMS may be capable of differentiating alterations to resin in future studies. Further development of GCˆGC-TOFMS methods for archaeological applications will provide a valuable tool to uncover significant information on prehistoric technological changes and cultural behavior.

Residue analysis has become a frequently applied method for identifying prehistoric stone tool use. Residues adhering to the stone tool with varying frequencies are interpreted as being the result of an intentional contact with the worked material during use. Yet, other processes during the life cycle of a stone tool or after deposition may leave residues and these residues may potentially lead to misinterpretations. We present a blind test that was designed to examine this issue. Results confirm that production, retouch, prehension, haft-ing, various incidental contacts during use and deposition may lead to residue depositions that significantly affect the accurateness of identifications of tool-use. All currently applied residue approaches are concerned. We therefore argue for a closer interaction with independent wear studies and a step-wise procedure in which a low magnification of wear traces is used as a first step for selecting potentially used flakes in archaeological contexts. In addition, residue concentrations on a tool's edge should be sufficiently dense before linking them with use.

After discard, archaeological stone tools are subjected to post-depositional processes, which may lead to an alteration of their surface state and thereby affect potential wear traces and residues. In spite of the durability of stone tools, the environment in which they are deposited will have an impact up until the moment an equilibrium is reached between the stone surface and its environment. This process will directly affect the wear traces formed on the stone tool during its use cycle, but also possible residues (depending on their nature, their degree of adhesion, etc.). Alterations have hampered functional analysis since its beginnings. Indeed, altered tools have been either misinterpreted or excluded from functional studies, creating a potential bias in the understanding of an archaeological assemblage or site. In this study, we focus on one process, the effect of freeze-thaw cycles on the preservation of use-wear traces and residues on stone tool surfaces.