Remodelling the past - Archaeometrological analysis applied on Birka weight material using a 3D scanner & Computer-Aided Design

Archaeometrological analysis has traditionally involved reconstructing the originally intended mass of a weight by hand; measuring with a calliper or a profile microscope, as well as using the artefact's displacement in water for factors such as volume and density. Ideally, corrosion was to be left intact, which is inconsistent with the goals of the conservationist. In all, the process was time consuming and may in some cases even have accelerated the deterioration of the artefacts. The CAD-method described in this article has been developed as a non-destructive alternative, employing a 3D scanner to create a virtual representation of the weight on which analysis can be performed. Density is calculated by dividing current mass with current volume, as supplied from the virtual model. Original volume is calculated by reconstructing the weight using basic geometrical shapes in a Computer-Aided Design program. Finally, to obtain the weight's original mass, the recreated original volume is multiplied by its current density. If the latter is found to have been altered through corrosion, a mean value of previously analysed weights in good condition (MNCA) may be applied instead. This new method for archaeometrological analysis is put to the test on a population of weights excavated at Birka. Four of these were previously analysed with the Traditional method, which makes it possible to compare results and draw conclusions on the accuracy of the CAD-method. An additional seven weights were analysed for further evaluation and also to investigate Sperber's theory of a 4.0 g standard unit in the metrology of Birka.