This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)
Researchers at the Institute for Integrated Research in Materials, Environments, and Societies (IIRMES), California State University - Long Beach (CSULB) will use NSF Major Research Instrumentation funding to develop a new instrument for dating prehistoric ceramics. Results obtained by materials scientists indicate that low-fired ceramics, such as bricks, tiles, and pottery, gain weight and expand by a process of water absorption that is highly regular on time scales from weeks to millennia. The age of a low-fired ceramic can thus be obtained via highly precise measurement of initial weight, followed by dehydroxylation (firing above 500oC), followed by precise monitoring of weight gain over five to ten days in order to establish the rate of rehydroxylation. The proposed new instrument will automate these steps within a controlled environment to enable large numbers of ceramics to be dated at low cost. In archaeology, determination of the age of artifacts is central to the success of the discipline. Over the years, archaeologists have made use of a wide array of dating techniques: radiocarbon dating, luminescence dating, tree-ring dating, obsidian hydration, electron spin resonance, uranium/thorium series dating and so on. Each technique is best for particular materials and particular time ranges. Ceramic technology was invented independently in multiple world regions during the past 10,000 years, and, since ceramics are durable, archaeologists routinely find broken pieces of pottery, tiles, bricks, and figurines by the thousands (or more) on archaeological sites in many regions of the world. Effective techniques for dating ceramics are thus particularly valuable for the discipline. Unfortunately, however, luminescence, the main technique currently used for dating ceramics, is relatively difficult and expensive. Initial experiments have shown that the rehydroxylation method promises very high precision with relatively simple measurements and instruments. Configured for large numbers of simultaneous measurements, rehydroxylation has the potential to reduce per sample cost dramatically, thus dramatically increasing the number of dates that can be run on any given archaeological project. Moreover, the relative simplicity of the instrumentation means that it could be disseminated to a wide range of laboratory settings. The NSF-supported project being undertaken at IIRMES-CSULB seeks to develop instrumentation and protocols that are optimized for efficient production of rehydroxylation measurements on ceramics. The automated instrument system will retain the precision of the rehydroxylation dating method while dramatically increasing the rate of sample throughput. The project directors anticipate that the new instrumentation will have important, even revolutionary, impacts on archaeological research.
Rehydroxylation (RHX) is a chemical process in which chemical forms of water molecules known as hydroxyls (chemically defined as OH) are adsorbed into the ceramic body that forms as a result of firing clay to high temperatures. The rate of rehydroxylation has a power-law relation with time; samples changing due to rehydroxylation will increase in weight due to the adsorption of OH as a function of time to the quarter-power (i.e., t1/4). This effect results in weight gain for a sample that is initially quite large and thus measurable. Measuring the weight of a ceramic sample before and after reheating to 500°C provides an estimate of the amount of OH adsorbed since the clay was first fired. Then, by determining the subsequent rate of rehydroxylation, one can learn how much time has passed since a sample was originally fired. Recently, material scientists (Wilson et al 2009) proposed that this process – now known as RHX dating – offers a new means of generating chronological information for archaeological pottery samples. The approach is particularly exciting since it relies on relatively simple measures (i.e., weight change). Thus, the method offers a means of dating the manufacturing event of artifacts and can be accomplished for low-cost and with high precision. RHX dating also has an advantage over traditional methods of dating ceramics such as radiocarbon dating since the event dated is directly related to the artifact’s history and does not require complex calibration. Finally, the technique is relatively non-destructive as the samples are only reheated and weighed. The present NSF project focused on the design, assembly, and creation of the basic infrastructure necessary to routinely make measurements for rehydroxylation dating of ceramic artifacts. Our project goals included work in three areas. First, we planned to acquire the necessary instrumentation to replicate the pioneering work of Wilson and colleagues (2009) and to establish baseline measurements for the procedure. Second, we planned to construct a low-cost, automated sampling system that can be implemented in any laboratory and that is capable of tracking, manipulating, and measuring 50 or more samples at a time under constant humidity and temperature. Third, we planned to run experiments designed to determine the boundary conditions, if any, under which the measurement of rehydroxylation produces reliable estimates of the date of firing. Overall, we have successfully achieved the goals of the project. We have a working facility at California State University Long Beach in the laboratories of the Institute for Integrated Research on Materials, Environment and Society (IIRMES) that can produce precise measures of changes in the weights of ceramics over time and under conditions of controlled humidity and temperature. We have found that the RHX method proposed by Wilson and colleagues works at least some of the time for New World archaeological pottery samples. This finding points to the great potential for RHX dating to open new avenues of research for archaeologists. Second, we have designed and created a relatively low-cost RHX measuring instrument with precise temperature and humidity control, database logging, and analytic tools. At the heart of the RHX instrument is an open hardware based auto-sampler that controlled via open-source software that tracks samples, logs measurements and integrates with the RHX measurement procedure to produce age estimations. The instrument is capable of tracking 50+ samples at a time in precisely controlled humidity and temperature environment. The system is designed with open-hardware and open-software design so that other researchers can easily implement it. In this way, the results of this project expand the potential impact of RHX dating for archaeological research. Finally, we have initiated experiments to explore the conditions under which the rehydroxylation dating method produces good estimates of firing age and the conditions under which it does not. These experiments have opened up new questions and new areas of research. For example, we have demonstrated that the method has complications when fired clay artifacts are from pottery vessels. Frequently, multiple sets of measurements on the sample ceramic sample will produce entirely different dates that are all too young or too old. We suspect that the addition of temper to the clay, calcium carbonate, and other non-clay minerals can contribute to weight changes that complicate the measurement of the effects of rehydroxylation resulting in erroneous ages. More studies are required to determine what physical and chemical treatments need to be done prior to measuring the rate of rehydroxylation. Thus, overall our findings point to the fact that significant additional work is needed to make RHX a viable and reliable dating technique for archaeological pottery. References Cited Wilson, M. A., Carter, M. A., Hall, C., Hoff, W. D., Ince, C., Savage, S. D., et al. (2009). Dating fired-clay ceramics using long-term power law rehydroxylation kinetics. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 465(2108), 2407–2415. doi:10.1103/PhysRevLett.90.125503
