Monday, October 1, 2012

RHX Dating Update

My collaborators and I mailed out some reports today about Fired Clay Ceramic Rehydroxylation Dating! I am pleased to say that we've completed our work that was supported by a small grant from the National Science Foundation's Division of Behavioral and Cognitive Sciences (Award #1112327) and an Fellowship Award to Patrick Bowen from the DeVlieg Foundation.

I know many people are very excited about RHX dating (and also very skeptical).  I was very excited about the proposed technique when it was published in 2009. This technique proposes to use the clock-like, nano-scale process by which water molecules bond with clay mineral crystals.  By taking an old ceramic sherd, heating it to remove any mass caused by humidity (atmospheric water), measuring it's mass, then firing the sample at a higher temperature to drive off all the rehydrated (adhered) water and rehydroxylated (chemically bonded) water, one can measure the sample's mass without any water present.  After that, carefully tracking the mass of the sample as it quickly starts to reabsorb water from the air allows you to generate an equation that models the time past, the water mass gained, and the rate at which this occurs.  So long as you can match the temperature in the room to the average lifetime temperature of the object, a bit of math lets the lab technician calculate how long it took for the sample to reach the weight at which it was discovered by archaeologists. All my posts about RHX dating are all here.

In 2010, we applied for an NSF grant to study this process and see if we could replicate the findings of the UK researchers that had proposed it.  We did win that grant, but we did some background work and tried to replicate their study. We published our results in 2011.  With that publication under our belt, we reapplied to NSF for more funding to upgrade our lab equipment to match the quality of that being used by the UK team.  At first, we were rejected, but then the NSF found a bit of money that allowed us to improve our instruments.  Using that grant, we purchased a new Citizen CM11 Microbalance along with a Coy Humidity Control Glove Box. This microbalance allows us to measure 0.001 mg of variation in mass, fully two orders of resolution and sensitivity higher than the balance that was available at Michigan Tech before the NSF award! It's was a lesser piece of equipment than we'd hoped to purchase, but it has permitted us to take our experiments to the next level of research quality.

In November-December 2011, We tested the station to determine the stability of humidity and temperature within the box as well as the stability of microbalance while it is reading in the box chamber environment. Between December 2011 and August 2012, Jarek and Patrick collected and analyzed the mass-gain data corresponding to rehydration/rehydroxylation of Davenport sherds and some brick samples from Houghton, Michigan.  After running tests on intact sherds, we also ran some pulverized samples. Jarek and Patrick worked over the data to examine the influence of relative humidity on mass gain and time curves.  From that analysis, we just submitted an article for review and publication. This one deals with the question of which model (expressed in an equation) best describes the samples behavior as they rehydrate and rehydroxylate over time. We also raised some questions about the micropore structure of the sherds and how that influences the model.

Figure 2 is from our report to NSF. It shows the fractional mass versus time obtained for the Davenport pottery sample under constant temperature and humidity (plot on the left hand side). 
Figure 2. Compiled fitting results for intact Davenport sherd in both linear time (left column) and time1/n with n= 3.77 (right column). Results were obtained at 22oC and 20%RH.
                  The right-hand plot in Figure 2 also shows the resulting theoretical fit using the following empirical equation describing the mass gain (m) (or fractional mass gain):

where t is the time, β is the term representing physically bonded water, α is the rehydration kinetics term, γ is the rehydroxylation rate, and n is the rehydroxylation exponent.  

Agreement between experimental data and theoretical model is remarkable!  

We found problems that present the researchers with challenges to making RHX a standard archaeometric tool for dating fired clay ceramic artifacts.  I will write more about those in another post, but I can't say too much until our article is published. I'm also excited to report that our initial success led to a new award from NSF (BCS-1219540)!

Our new collaboration will allow our team at Michigan Technological University to coordinate an experiment involving five different international teams of faculty and students (Michigan Technological University, Arizona State University, California State University-Long Beach, Tel Aviv University, and The University of New England) working on new RHX experiments, advised by a team of UK scientists, many of whom initially proposed this technique, and continue to work on it's refinement (Universities of Manchester, Edinburgh, and Bradford).  We will send a set of blind samples for testing to five labs including materials scientists and archaeologists from seven different universities in four countries. 

I am very excited!

Friday, April 27, 2012

GlobalPottery Conference

The Utah Pottery Project has been quiet for a while!  I've had other funded research and obligations mentoring graduate and undergraduate students.  Things have started to percolate again, however, so more may be forthcoming this summer!

Meanwhile, I am excited to attend next week's GlobalPottery conference. The meeting is subtitled the First International Congress on Historical Archaeology & Archaeometry for Societies in Contact.

For more than a decade, my colleagues and I have been talking about the growing interest in applying the tools of materials science and archaeometry to examine the global flows of pottery in the early modern and modern worlds.  We spoke about a number of challenges--the scale of the research area, the size of a database necessary to make meaningful statistical arguments, the movement of raw materials and skilled workers within and between geographic regions, the hesitancy to emphasize the value of scientific analysis vs. interpretive practice in American historical archaeology, and the reluctance of anyone to systematically dedicate real-dollar funds to support an overwhelmingly global scientific effort.

After so many years, we are finally going to gather and talk about the issues and perhaps develop a plan.  There has been a clear florescence of research in this area.  If you look at the scholars scheduled to present their work, and the content of their presentations, I think you'll agree that this will be an exciting meeting!

I am honored to participate and gratefully thank the Department of Social Sciences at Michigan Technological University. My department provided some of the financial support I needed to attend the meeting and speak about the Utah Pottery Project.

You can review the Congress program and speakers here: