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 time^1/n with n= 3.77 (right column). Results were obtained at 22^oC 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!

News update: the good, the bad, and the ugly.

The good news:

Now that the academic semester is almost at an end, I will spend a bit of time on the project preparing some artifacts for a new exhibition!  The Church of Jesus Christ of Latter-day Saints' Church History Museum is going to install a version of Potters of the Gathering in their lobby.  The exhibit will open May 7th.  Kirk Henrichsen is using pottery to remind people about nineteenth century foodways and domestic life, to explore the ideal of self-sufficiency in Latter-day Saint communities, and to show people how important archaeology is as a tool to increase our understandings of the past.

Mr. Henrichsen has gathered together some new material for this show.  He will be using most of the important objects from the original exhibit- including the Thompson Collection, the Utah State Parks Collection (including the Deseret Pottery artifacts), and the Utah Pottery Project collection.  He has also found some other cool items to include, such as a Deseret Agricultural and Manufacturing Association Medal from the Territorial Fair, which will be displayed with some award winning pots!  It should be a great show and will be the first time most of this material has been exhibited to the public in Salt Lake City.

The museum has invited me to give a talk at the opening and I am excited to see the new installation.

The bad news:

Both organizations declined the proposals I'd written seeking funds for more work.  One of the grants would have supported additional fieldwork. The other sought funds to allow more experiments to develop and refine ceramic rehydroxylation dating (RHX dating).  No matter how many times it happens, reviewers rejections always sting a little, even when accompanied by encouragement to "revise and resubmit."

Either way, the lack of support funds means that we will box up the artifacts and put more of the analysis on hold for the summer.  I'll be co-teaching the 2010 Industrial Heritage and Archaeology Field School this summer at the site of the Cliff Mine in Keweenaw County in Michigan's Upper Peninsula.

I'll continue to collaborate with my friends in Materials Science.  Since Patrick Bowen was awarded two grants for undergraduate research, we will move as far ahead as we can investigating reydroxylation.  I think he will work with Jarek Drelich to characterize the clay and ceramic used by the Davenports and try to figure out the significance of the different water-absorbtion processes at work in ceramics.

We'll reflect on the reviewers' comments for a few days and then meet to plan the strategy for the rest of the summer and the fall term.

Congratulations to Patrick Bowen

I am pleased to congratulate Patrick Bowen, Michigan Technological University undergraduate student in Materials Science and Engineering.  Mr. Bowen won two major fellowship competitions and he was awarded funds for his ongoing collaborations studying rehydroxylation dating of archaeological ceramics.  He was awarded one of Michigan Tech's Summer Research Experience for Undergraduates (SURF) Fellowships as well as a Michigan Space Consortium Undergraduate Research Fellowship.

Patrick has been an important part of the interdisciplinary research team that Jarek Drelich and I put together to assess this newly published dating technique.  Mr. Bowen, Helen Ranck, and Jessica Beck, three MTU undergraduates in the Departments of Materials Science and Social Science, did exceptional work designing tests to assess the usefulness of RHX Dating for the Utah Pottery Project.  Patrick is presenting the preliminary results of their analysis at MTU's 2010 Undergraduate Research Expo.

The SURF and MSC Fellowship programs are both very competitive and I am proud of Mr. Bowen for his successful applications!

We are waiting to hear decisions on the proposal I wrote to support more field research as well as a National Science Foundation proposal to support more research into Rehydroxylation Dating.

I'm keeping my fingers crossed on our outstanding proposals!

Rehydroxylation Dating-- 10-21-09 update

Our collaborating student researchers are making steady progress in their efforts to replicate the ceramic rehydroxylation dating technique published by Moira Wilson and her colleagues over the summer. If you wish to read all my posts about rehydroxylation, click here.

Helen Ranck, Patrick Bowen, and Jessica Beck have been working on different parts of the problem and they've learned a great deal so far.

Here is one of Helen's graphs that describes the mass gain of one of her test samples:

She and Patrick have been trying to find out the best way to keep the sherds at a constant temperature and atmosphere while the fragment absorbs water. Patrick has discovered some key changes in practice that have really helped reduce the variation in calculated dates, bringing the projections closer to our expectations. Jarek Drelich, associate professor in Michigan Tech's Materials Science and Engineering department, has been very helpful working with them both.

Jessica Beck has finished some of her testing. She calculated the porosity of a group of the sherds using a methodology outlined by the National Institute of Standards and Technology (NIST). Jessica discovered that the Davenports' earthenware ranges from 10%-15% porous, and that both the median and the mode will be around 13% or 14%. I'm looking forward to her final conclusions and her estimates on firing temperature as revealed through her other testing!