Optical Profilometry as a Non-Destructive Technique to Quantify Engraving on Medieval Brass Astrolabes

摘要

Optical profilometry has been performed on an astrolabe dated 1556 AD and attributed to the famous maker Gualterus Arsenius of Louvain, Belgium. In this non-destructive technique, a beam of white light is impinged on the sample and combined with the chromatic aberration technique to accurately measure surface features. With machine parameters set to a vertical resolution of 0.1μm, lateral resolution to 6 μm and a 3 mm depth of field, various engraving features on the astrolabe were studied. Both hand-scribed and stamped markings are present on the astrolabe components. Inspection of the hand-scribed date on the instrument's mater allows one to quantify the shape and dimensions of the tool used, as well as the direction and inclination of the engraving tool during inscription. The results of this analysis give information about how the astrolabe was constructed in one of the Renaissance's greatest scientific instrument workshops. The results are compared to similar engravings on an undated and unsigned Islamic astrolabe tympan.