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CBM Method mindmap - Coggle Diagram
CBM Method mindmap
pXRF
Soil vs Mining mode
Soil has no LE, and targets heavy elements
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Offcuts vs tiles
Previous pXRF analyses on CBM from Roman Britain have analysed multiple points (usually 3) on the surfaces of tiles
Not possible here as RB assemblage presents considerable traces of surface concretions, in some cases up to 20mm thick, due to post-depositional environments
Moreover, previous analyses have not distinguished between the analysis of flat, combed or sanded surfaces. May seem to be a pednatic distinction, but pXRF is fundamentally a surface technique with majority of x-ray derived from less than 1mm depth
While the analysis of moulding sand, concretions or traces of mortar in previous studies may not have affected overall results, it is unclear to what extent this could have affected analyses especially when averaged
Decision taken to analyses only fresh breaks and offcuts made during visual analysis for this study as a way to test if tighter control of sample points, free of mortar, moulding sand and generally concretions, could provide more robust data and better sample grouping than that observed in previous work
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Generally, only one offcut taken per sherd. Each measurement only captures a small degree of sherd variation therefore compared to multiple analyses on same sherd
This cannot be helped. Repeat measurement of the same points on offcuts conducted to ensure that the data is representative of this point, as significant variation in quantities of light elements observed even for the same spot analysed on actual offcuts
Analysis of only a single offcut for most sherds means that emphasis is on chemical variation within 'groups', not on the chemical data derived from only a single sherd
To this end, far larger number of samples will be incorporated in the study than in previous analyses to achieve this wider perspective
Why pXRF?
Elemental characterisation presented an important opportunity to test CBM at another scale beyond visual/micro characterisation
Unfortunately, conventional ED-XRF, WD-XRF not available
XRD was considered, but although facilities exist no opportunity for training presented itself so was excluded from analyses
SEM-EDS a possible way for chemical characterisation, but due to sample prep methods would have been limited to only a tiny sample of assemblage
pXRF, despite perception as a non-invasive portable technique, therefore selected as rapid analyses, can be deployed in a lab, and sample prep can be minimal, as well as having green tech status