Experimental replication of Australian grinding stone implements

Introduction:
Until recently, lithic tool-use experiments in Australia were dominated by flaked stone with relatively few studies of ground-stone. This paper reports on a workshop, during which tool-use experiments were designed to document the wear traces associated with grinding various materials, different processing techniques and sandstones of different hardness. The specific variables were selected to build a use-wear and residue reference library applicable to archaeological grinding implements proposed for detailed functional analysis.
Materials/Methods:
Experimental sandstone grinding implements were used primarily to process organic and inorganic materials, documented ethnographically. Other materials were processed to investigate characteristics of seeds that were unavailable locally. Upper and lower stones were used together to grind seeds and bone; and abrading stones were used to file bone, stone and wood, and to grate haematite. The experimental stones came from five geographic regions in Australia, each associated with the archaeological assemblages proposed for study. Usewear was sampled with polyvinyl siloxane peels, which were examined under a stereomicroscope and a metallographic microscope. Residues were extracted with two solvents (water and a tri-mixture of acetonitrile, ethanol and water), and subsequently mounted on slides and examined under transmitted light microscopy. The slide preparations were stained to highlight constituent plant and animal tissues.
Results:
The hardness/softness of the sandstone and the degree of grain cementation have a strong influence on the development and appearance of use-wear. On the hard sandstone, the processing time affected polish formation. Use-wear patterns were distinctive of the broad categories of processed material (seed, bone, stone, haematite and wood). Key use-wear features relating to activity and processed material are reflected in the degree of grain rounding and grain levelling, the presence of macroscopic surface striations and the occurrence of micro-fractures, polish and striations observed at high magnification.
Residues included collagen and cellulose fibres, starch granules, phytoliths, resins, bone fragments and pigment crystals. As for use-wear, the residues were also distinctive of the broad categories of processed material. Staining was particularly useful to distinguish plant and animal tissues.
Conclusions:
The experiments provided insights into the wear formation on sandstones of different hardness and degree of cementation. Stained cellular structures provide a reliable basis for distinguishing the investigated plant and animal tissue subjected to mechanical damage, resulting from grinding and pounding. Studies are underway to further test the viability of residue identification on ethnographic specimens of varying ages, and experimental grinding stones greater than 30 years.
The residue and usewear experiments build on previous studies and help form the basis of a systematic and collaborative use-wear and residue reference library for ground-stone tools in Australia. Future experiments will focus on the wider range of plant taxa processed by grinding and documented ethnographically.