CAA2016

A Comparison of Methods for Creating 3D Models of Obsidian Artifacts

Samantha Thi Porter, Kele Missal

Abstract
Within the discipline of lithic analysis, digital 3D artifact models are useful both as a means of augmenting traditional two-dimensional representations, and as a form of raw data for morphometric and technological analysis. Unfortunately, some raw materials are inherently more difficult to capture than others. Obsidian, specifically, is highly reflective, tends to have a visually homogenous surface, and is oftentimes transparent. All of these factors restrict a researcher’s ability to capture images of obsidian objects that are of high enough quality for the construction of an accurate 3D model. In some parts of the world the vast majority of lithic artifacts are made of obsidian. Therefore, finding a way to systematically model obsidian artifacts with a high degree of precision would be extremely useful.

We compare the effectiveness of two different methods of capturing object morphology, (structured-light scanning using a DAVID SLS-2 system and close-range photogrammetry using the software Agisoft PhotoScan) in conjunction with several commonly used substances used to coat lithic artifacts for scanning, (brushed-on talc powder, talc-based developer spray, and chalk spray) on a sample of experimentally produced obsidian pieces of different shapes and sizes. Coatings are evaluated on their ease of use, the quality of scans that result from their use, and their impact on artifacts (e.g. difficulty of removal, and effects on artifact labels). The quality of the 3D models are evaluated on the accuracy of gross artifact morphology as well as success in capturing fine features commonly used in lithic analysis such as retouch, platform preparation removals, ripples, and lancets. We also discuss alternative methods of documenting obsidian artifacts that do not necessitate coating, such as Reflectance Transformation Imaging (RTI).