X-ray powder diffraction clustering and quantitative phase analysis on historic mortars

Abstract

This paper describes the application of cluster analysis to X-ray powder diffraction patterns (XRPD) to define homogeneous groups of mortar-based materials according to their mineralogical composition. For this purpose, the diffraction patterns of 110 samples of mortars from the Temple of Venus (Pompeii, southern Italy) were used to test the method. Rietveld refinement, for quantitative mineralogical phase analysis, was performed on the most representative sample of each cluster. The mineralogical grouping yielded by cluster analysis of XRPD data turned out to be consistent with the petrographic groups.

Non-Destructive Multi-Analytical Approach to Study the Pigments of Wall Painting Fragments Reused in Mortars from the Archaeological Site of Pompeii (Italy)

“…In recent years, there has been growing interest in ancient Roman technology which has led to the publication of several archaeometric studies on the raw materials used for the construction of buildings and on the artistic handicrafts made in the ancient city of Pompeii [6][7][8][9][10][11][12][13][14].…”

How to Estimate the Binder: Aggregate Ratio From Lime-Based Historic Mortars for Restoration?

“…Thus, the binder: aggregate ratios were 1:1.5 and 1:10.3 for Arquivo Público and Casa Quintino, respectively (Figure 3). The statistical indices show that the Rietveld refinement for samples without an internal standard was not so satisfactory when compared to another study developed by Piovesan et al, 2013, in which the R wp indexes varied from 6.5 to 11.5, which may indicate that the proposed refinement for the mortar samples from Belém do Pará did not achieve good results, which the R wp were 14.2 and 13.5 for Arquivo Público and Casa Quintino, respectively. On the other hand, it is known that the low values of the error indexes do not always indicate the best refinement, as this is only one of the criteria to evaluate the quality of the Rietveld refinement, and it is also necessary to have a great value graphic analysis to verify if there is a good refinement (Toby, 2006).…”

Cluster analysis of XRPD data in ancient ceramics: What for?

“…These choices were made according to the evaluation proposed by Piovesan et al (2013), with different metrics and linkage criteria on the same set of samples. Euclidean distance was preferred to squared Euclidean distance, since the latter is used to place progressively greater weight on objects which are farther apart.…”

“…Unlike chemical data, on which multivariate statistical tools have long been applied in studying ancient pottery (methodological papers: Mommsen et al, 1988;Tangri and Wright, 1993;Baxter, 1994Baxter, , 1999Baxter, , 2006Baxter, , 2008Neff, 1994;Buxeda i Garrigós J., 1999;Baxter and Buck, 2000; some case studies: Maritan, 2004;Maritan et al, 2013;Holakooei et al, 2013;Baklouti et al, 2015), cluster analysis has only recently been applied to XRPD data in archaeometry, to study the production recipes of ancient mortars (Piovesan et al, 2013) and in the geological field, for grade control of iron ores (Paine et al, 2012); principal component analysis has been performed on Iranian tiles (Holakooei et al, 2014). The great potential of cluster analysis of XRPD data is that it can compare the similarity of the whole dataset, through the "figure of merit", which quantifies matching among scans and does not require a priori quantification of the phases composing each sample.…”