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Assessing and correcting the effects of the chemical weathering of potsherds: A case study using soft‐paste porcelain wasters from the Longton Hall (Staffordshire) factory site
Author(s) -
Owen J. Victor,
Day Terence E.
Publication year - 1998
Publication title -
geoarchaeology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 44
eISSN - 1520-6548
pISSN - 0883-6353
DOI - 10.1002/(sici)1520-6548(199802)13:3<265::aid-gea2>3.0.co;2-2
Subject(s) - wollastonite , weathering , leaching (pedology) , mineralogy , dissolution , geology , metallurgy , materials science , chemistry , geochemistry , soil science , soil water , raw material , organic chemistry
Unglazed soft‐paste porcelain wasters from the Longton Hall factory site are variably depleted (75–80 rel %) in CaO relative to comparatively insoluble components (e.g., Al 2 O 3 , TiO 2 ) due to the dissolution of wollastonite (CaSiO 3 , a pyroxenoid) by subsurface water. The degree of desilicification is variable (0–45 rel % SiO 2 ). Petrographic data and element‐abundance plots suggest that these were the principal effects of the chemical weathering process in most samples. The preferential dissolution of a single phase in the unglazed Longton Hall sherds permits the semiquantitative “reversal” of weathering phenomena. Alteration effects can be corrected using porosity–volume data to constrain the amount of wollastonite originally present in the weathered sherds. The original compositions of the unglazed wasters are bracketed by arithmetically “adding back” the missing pyroxenoid components according to two endmember assumptions concerning element mobility: (1) the total leaching of wollastonite components and (2) the preferential leaching of wollastonite‐derived CaO. These calculations—particularly the latter—yield results that compare favourably with the compositions of relatively unaltered (wollastonite‐bearing), glazed samples from the Longton Hall site. Given the potential susceptibility of archaeological ceramics to chemical weathering, it would seem prudent that these phenomena be carefully assessed, and corrected where possible, so that analytical data for these artifacts can be judiciously interpreted. © 1998 John Wiley & Sons, Inc.