James Christopher Wilkins
Research student, Conservation, School of History, Archaeology and Religion
Portable X-ray fluorescence (PXRF) is advertised as a portable point-and-shoot method enabling non-destructive elemental analysis of objects. Its attributes and relative cheapness compared to other forms of analyses has seen its use in the cultural heritage sector dramatically rise over the past 10+ years without proper understanding of the mechanics involved. Ideal samples for PXRF analysis are homogenous, lacking weathering and surface deposits, and are infinitely thick with regards to incidental radiation penetration. These characteristics are rarely found with archaeological material. Faience glazes represent a layer on a body constructed from similar material. Discerning depth of analysis and knowing elemental sources (glaze or body) detected with PXRF on archaeological faience is difficult to impossible without an evaluation. It is common for faience glazes to exhibit corrosion manifested by de-alkalized glaze in a thin layer near the surface and along crack faults. The glaze is heterogeneous containing pores, partially sintered quartz particles and other inclusions. Surface deposits (i.e. soil from the burial matrix) will attenuate the incidental radiation and add peaks to the analytical spectra. All these characteristics will result in false compositional data. Quantified data resulting in elemental weight percents is expected with PXRF systems but are dependent on the analysis of several controls (e.g. standard reference materials and/or minerals), materials whose cost are prohibitive to most PXRF users.
This project will provide a PXRF methodology for the analysis of applied blue faience glazes. Net peak analysis will be used on Corning Glass B to determine best parameter setup and methodology for elements of interest. Replicated and archaeological faience will be analysed using the resulting methodology. Depth of measurement will be determine through theory and replicated material analysis. An emphasis will be placed on trace elements to determine if faience groupings can be discerned from the analysis. This information may be useful in future research regarding attribution to individual workshops and proveniencing of raw material. Scanning electron microscopy (SEM) will be used to calculate fractionation of the replication faience components during firing and determine if an approximation of original recipe can be deciphered through the analysis. Principle component and clustering analysis of SEM and PXRF data will be compared to determine if the analyses are comparable. The results of the study will be useful to conservators, curators and field archaeologist, and other parties interested in the analysis of glazes.
- Scanning Electron Microscopy
- Portable X-Ray Fluorescence
- Experimental Archaeology
- Field Archaeology
- North American Archaeology
- Archaeological Conservation
- Statistics in Archaeology
- Culture Contact
Application Glazing of Late to Roman Period Faience from Egypt: Blue Glazes and an Evaluation of the Portable X-Ray Fluorescence Technique
The project will answer the following questions:
• Is portable X-ray fluorescence (PXRF) applicable to the study of faience glazes?
• Are scanning electron microscopy and PXRF results compatible?
• If so, what is an appropriate PXRF methodology for faience?
• What can archaeologist in the field expect from the use of PXRF on faience?
• Does spectroscopy provide an approximation of original recipe for similar glazes?