The effect of numerical aperture on quantitative use-wear studies and its implication on reproducibility

Abstract

Many archeologists are skeptical about the capabilities of use-wear analysis to infer on the function of archeological tools, mainly because the method is seen as subjective, not standardized and not reproducible. Quantitative methods in particular have been developed and applied to address these issues. However, the importance of equipment, acquisition and analysis settings remains underestimated. One of those settings, the numerical aperture of the objective, has the potential to be one of the major factors leading to reproducibility issues. Here, experimental flint and quartzite tools were imaged using laser-scanning confocal microscopy with two objectives having the same magnification but different numerical apertures. The results demonstrate that 3D surface texture ISO 25178 parameters differ significantly when the same surface is measured with objectives having different numerical apertures. It is, however, unknown whether this property would blur or mask information related to use of the tools. Other acquisition and analyses settings are also discussed. We argue that to move use-wear analysis toward standardization, repeatability and reproducibility, the first step is to report all acquisition and analysis settings. This will allow the reproduction of use-wear studies, as well as tracing the differences between studies to given settings.

Rethinking Use-Wear Analysis and Experimentation as Applied to the Study of Past Hominin Tool Use

“…This approach has now reached a high degree of sophistication in the field, for both experimental and archeological samples (Stemp 2014). Since quantification methods have comparison and frames of reference as their main goals, researchers have realized that it is fundamental to define standards and protocols that improve data repeatability, reproducibility, and comparability (Adams 2014;Calandra et al 2019b;Dubreuil and Savage 2014;Evans et al 2014). This is of particular importance since different pieces of equipment are used by various researchers, and different settings can be applied during the analysis (Stemp et al 2013(Stemp et al , 2018.…”

“…Similar discussions have also taken place, for example, in dental microwear studies, where researchers have shown that dental microwear patterns correlate with diet. In archeological samples, the variation in wear patterns emphasizes the need for protocols, standardization, and quantitative methods when documenting and measuring surface textures (Calandra et al 2019b).…”

Polish is quantitatively different on quartzite flakes used on different worked materials

“…Our analyzed surfaces (sub-areas) are 50 x 50 μm, as in Evans et al [20]. The optical lateral resolution of the 50x/0.95 objective is high (see Supplementary Material 1 of [38] but the digital resolution (= pixel size) is too low (0.25 μm) to allow smaller areas to be analyzed. On the other hand, larger areas do not fit on the quartz grains of these quartzite varieties.…”

“…Therefore, all data are fully accessible, and different surface analysis workflows and statistical comparisons will be possible with future research. Moreover, the full reproducibility of data acquisition is guaranteed by the reporting of the acquisition settings of the microscope used in this paper [37,38].…”

“…The main underlying goal of doing this is to limit the analysts' subjectivity and to increase the general accuracy of the method [6,37]. Moreover, it improves repeatability and reproducibility of the analyses [38]. However, it has been shown that it is not yet possible to automatically locate and isolate the worn areas (i.e.…”