The effect of worked material hardness on stone tool wear

Abstract

The identification of ancient worked materials is one of the fundamental goals of lithic use wear analysis and one of the most important parts of understanding how stone tools were used in the past. Given the documented overlaps in wear patterns generated by different materials, it is imperative to understand how individual materials' mechanical properties might influence wear formation. Because isolating physical parameters and measuring their change is necessary for such an endeavor, controlled (rather than replicative) experiments combined with objective measurements of surface topography are necessary to better grasp how polish formed on stone tools. Therefore, we used a tribometer to wear natural flint surfaces against five materials (bone, antler, beech wood, spruce wood, and ivory) under the same force, and speed, over one, three, and five hours. The study aimed to test if there is a correlation between polish formation and the hardness of the worked material. We measured each raw material's hardness using nano-indentation test, and we compared the surface texture of the polished flint bits using a 3D optical profilometer. The interfacial detritus powder was analyzed with a scanning electron microscope to look for abraded flint particles. We demonstrate that, contrary to expectation, softer materials, such as wood, create smoother polishes than hard ones, such as ivory.

The role of artificial contact materials in experimental use-wear studies: A controlled proxy to understand use-wear polish formation

“…The first rapid increase in surface roughness documented on most samples could be explained with initial abrasion processes (Schmidt et al, 2020) removing the surface created by the saws and leading to a temporary state of a more "natural" surface. The subsequent decrease in surface roughness is in accordance with the data from other similar studies (Ibáñez and Mazzucco, 2021; see also Rodriguez et al, 2021).…”

“…At the same time, the use of natural contact materials seemed to favour wear formation in comparison to the tested artificial contact materials when considering the quantitative data only. While some contact materials as for instance antler, bone and ivory as one category, or especially cereals as another, leave distinguishable and identifiable use-wear traces (Stemp, 2014;Ibáñez et al, 2014;Ibáñez et al, 2016;Pedergnana et al, 2020a;Ibáñez and Mazzucco, 2021;Rodriguez et al, 2021), others such as meat and hide do not. Correspondingly, the study shows that the visual appearance of the use-wear traces on experimental samples differs for the soft and hard contact materials (Fig.…”

“…Perhaps due to the machine-cut surfaces of the experimental standard samples, the processes and resulting patterns of surface texture modifications are complex, making it nearly impossible to determine the cycle based on the quantitative data. Especially for samples used on soft contact material, this problem is also known for samples with a natural, knapped surface (Ibáñez and Mazzucco, 2021;Rodriguez et al, 2021). Depending on the stage of development, worked material can only be identified with a low degree of confidence due to the problem of similar surface characteristics and thus an overlap of unused and used areas.…”