Rehydration/Rehydroxylation Kinetics of Reheated XIX-Century Davenport (Utah) Ceramic

Abstract

Rehydroxylation (RHX) dating has recently been proposed as a new chronometric dating tool for use on archeological fired-clay ceramics. The technique relies upon the well-known characteristic of reheated porous ceramic vessels to regain water through a two-stage process (rehydration and RHX), where the kinetics of second stage has been shown to follow a (time) 1/4 power law at temperatures of 131-501C. In this study, experiments were conducted in which the mass measurements taken from 19th-century ceramic artifacts could be described by the (time) 1/n power law over a wide range of temperatures. This finding has led to the formulation of a new empirical equation, which describes the observed ceramic's rehydration and RHX behavior without the need for identification of RHX stage. As part of this study, the mineralogy of the ceramics and their thermal properties have been evaluated. The instantaneous effect of humidity on mass measurements was demonstrated to be the principal source of error. RHX dating shows promise, and after more research, the technique could become an important archeometric tool.

Experimental Variability in Kinetics of Moisture Expansion and Mass Gain in Ceramics

“…Moreover, RHX datasets obtained over several weeks by Le Goff and Gallet from fired‐clay (pottery and bricks) samples of different ages and geographical origins showed mass variations behaving according to a t 1/ N power law, in agreement with H2011, except that N varies between ~3 and ~5 [see also Ref. )]. The divergent values of N could explain both the concave and convex mass‐gain behaviors recently described by Wilson et al .…”

“…Since the seminal article of Wilson et al ., other groups around the world have tried to reproduce this method, but without success [e.g., Ref. )]. These studies highlighted several complexities with the method and in particular, the foundation of the RHX dating method itself, that is, the universality of the t ¼ time power law …”

Composition, Microstructure and RHX Dating of Romanesque Relief Ceramic Tiles

“…This method was proposed as self-calibrating without any standardisation and, thus, neglects the influence of firing temperature or mineralogical composition as demonstrated in Wilson et al [23]. The futher testing of this method on real samples showed the need for further investigation, especially in connection with the mineralogical composition and storage conditions [24][25][26][27][28][29][30].…”

“…These samples were dried at 105 ± 2°C to a constant weight (usually for 24 hours) in the BMT Venticell 55 laboratory and weighed using an AND GR 200 analytical balance, with a precision of 0.1 mg. Then the samples were reheated in a CLASIC laboratory furnace at 650°C for 12 hours to release all chemically bonded water [11,[24][25]. The reheated samples were placed on a measuring cell of the analytical balance in an enclosed measuring box with a stable controlled temperature (19 ± 1°C) and relative humidity (30 ± 2 %).…”

Reproducibility in Rehydroxylation of Ceramic Artifacts

“…Only poorly reproducible results were reported so far, with many requiring variations on the original ¼ power law. In our previous contributions, we have used a generalized power law ( 1/n ) with a variable exponent ( n ), to describe the RHX behavior of ceramics without identifying their ages . The ∆ m versus 1/n curves produced for several samples demonstrated improved linearity in RHX Stage II …”