Near-Infrared Reflectance Spectroscopy for the Analysis of Mortar In the House of the Vestals, Pompeii, Italy

The ruins of Pompeii, having been so well preserved, allow a unique opportunity to study architectural styles, techniques and materials on a large scale. Traditional geochemical analysis is inherently destructive, and collecting samples of construction mortar, no matter how small, will irreparably damage the walls. This study aims to test a method of portable analysis that can be used to analyze the mortar in situ, eliminating the need for destructive sample collection.

To establish a known compositional profile, samples were collected from the House of the Vestals, a large, elite house in Pompeii, Italy. X-ray fluorescence (WD-XRF by borate fusion method) analyses revealed the mortar was a mixture of lime-based cement (~18% CaO) and reddish volcanic sand containing ~36% SiO2, ~15% Al2O3, ~4% MgO, ~4.8% Fe2O3, ~3.5% K2O, and ~2.1% Na2O. Thin section analysis and X-ray diffraction of selected samples revealed the lime was composed of calcite and vaterite, and the volcanic material contained well-formed clinopyroxene, plagioclase and olivine crystals.

Field analysis techniques included imaging with a portable microscope and short wave infrared reflectance spectrometry (SWIR) with the FieldSpec 3 spectroradiometer. The short wavelength range is useful for analyzing and identifying carbonates, making this equipment ideal for the material under study here. Portable SWIR initially provides qualitative mineralogical data, but these can be quantified to determine chemical composition as well. In order to compare the initial results to those obtainable with the portable equipment, the portable technique was tested both in the field on the in tact mortar and in the lab on collected samples.