Abstract
A recently published analytical technique to detect chloride ions in ceramic vessels that were used to produce salt is replicated (Horiuchi et al., 2011). The method involves releasing bound chloride ions permanently retained by the vessel via a chemical exchange reaction with ammonium fluoride, following the removal of all unbound salt with water. The chloride concentration is measured in solution and used to quantify the amount of salt that was bound to the ceramic matrix. Our data suggest that this method is not a viable way to consistently discriminate salt-making pottery, as the detected chloride may not be derived from salt production activities, but from the ceramic material of the pot itself. We employ experimental vessels in which salt-making was simulated, in addition to analyzing excavated sherds from two Chinese and one North American site known to have been involved in salt production. The method proposed by Horiuchi et al. is not able to distinguish salt-making and non-salt-making vessels from one another.
Highlights
There is currently no low-cost method to unambiguously identify salt production pottery
This is necessary for two potential reasons: (a) salt may have been introduced into the ceramic matrix postdepositionally, and is unrelated to the function of the vessel and must be removed, or (b) salt introduced into the ceramic during salt production that remains soluble may be removed during burial in the ground and is an inconsistent and unreliable marker
After all of the unbound chloride was removed by repeated washings with water and the measured concentration of chloride falls below the limit of detection of the probe, ammonium fluoride was employed in subsequent cycles (Fig. 4)
Summary
There is currently no low-cost method to unambiguously identify salt production pottery. The technique proposed by Horiuchi et al (2011) promised to allow for the inexpensive chemical detection of salt within salt-making vessels, and would have had great potential to impact work on the archaeology of salt production worldwide This study replicated this method using experimental pots and sherds from archaeological sites di↵erent from those of the original experiments. Horiuchi and colleagues proposed a method to retrieve water-insoluble chloride ions trapped within pottery matrices through the use of a relatively inexpensive chloride probe They created ceramics that were similar to vessel types in antiquity, used them to make salt, and subsequently washed them with distilled water to mimic the removal of chloride by natural percolation after use. We hoped to verify this method and further extend previous research on salt production at these sites and, in the case of Zhongba, expand on the limited but provocative chemical work done previously by comparing ceramics thought to have been used for salt making to those that were thought to be used for other purposes
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