A Primer on Sample Pretreatment

Earlier this month, Dr. Carla Hadden, a Research Scientist at the University of Georgia’s Center for Applied Isotope Studies, gave us a primer in how samples are pretreated prior to dating. In this post we’ll discuss how samples are prepared for taking radiocarbon measurements. Our next post will discuss the actual steps involved in radiocarbon dating.

Pretreatment is an essential step in the dating process. The main purpose of pretreatment is to remove contaminants from the material to be dated. In the case of bone samples, pretreatment includes extracting collagen, the material that is ultimately dated. Archaeological materials almost always include contaminants introduced by the materials that they were buried in or with, such as humic or fulvic acids in soil. Other sources of contamination can be introduced during the collection, conservation, or packaging of samples. These extraneous sources of carbon need to be removed in order to get an accurate measurement of the carbon absorbed by an organism during its lifetime.

First, let’s discuss the steps involved in the pretreatment of bone. This sample is a portion of a deer long bone from the bone from the Orion site in Ontario.


First, a subsample of the bone is cut away using a Dremel tool. That subsample is then cleaned using a scalpel and wire brushes in order to remove any surface contamination such as dirt and root fragments. It’s then gently broken down into pieces approximately 3-5 mm in size. The sample is then placed in a solution of hydrogen chloride (HCl). The HCl works on the material to demineralize it and extract collagen — which is what ultimately gets dated. The HCl and bone solution is kept cold in order to control the pace of the chemical reaction.


Dr. Hadden has to work fast to ensure that the collagen in the sample remains intact during the sodium hydroxide treatment

The acid is then decanted and the demineralized bone fragments are rinsed multiple times in ultrapure water. The bone fragments are then treated with Sodium Hydroxide (NaOH) to dissolve and remove contaminants such as humic acids. It’s then washed again in ultrapure water three times. The demineralized bone fragments were then rinsed again in HCl to eliminate atmospheric carbon dioxide that might be absorbed during pretreatment. They are then rinsed again in ultrapure water to and placed in a slightly acidic solution and heated at 80ºC for 8 hours to reduce the solution.

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Dr. Hadden places samples onto a hot plate so that the liquid evaporates gently, concentrating the collagen in the solution

The resulting solution is then filtered through a glass fiber filter to isolate the collagen that has been extracted. The collagen is then freeze-dried. At the end of the process, this collagen looks fluffy and crystalline, somewhat like cotton candy.

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The end result of the pretreatment process. Freeze-dried collagen.

The majority of samples we have dated thus far during the Dating Iroquoia project have been maize. Plant material goes through a different set of steps during the pretreatment process.

As with bone, the sample is cleaned under a microscope to remove dirt particles and extraneous material.

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Dr. Hadden cleans a maize kernel to prepare it for pretreatment.

The sample is then carefully split with a scalpel. The remainder of the sample is retained by the lab in case we need or want to run additional measurements on the material in the future. Sometimes it is very useful to have multiple dates from the same sample. Only a very small amount of material is needed for AMS dating and Dr. Hadden tries to take less than half so that a robust amount remains for future analysis.

Plant material goes through an acid/alkali/acid pretreatment. The plant material is then treated with HCl to remove carbonates and acids that might be present due to contamination. Since these materials can be of a different age than the sample itself it’s important to remove them before dating. The samples are then rinsed, treated with NaOH at room temperature to remove humic substances, rinsed again and then treated with HCl a second time, rinsed repeatedly with ultrapure water, and dried.

That’s it for the pretreatment process! In our next post we will talk about the next steps that happen in the lab and the actual process of radiocarbon dating.


April Adventures in New York

April was a busy month for the Dating Iroquoia team!

Samantha Sanft visited the New York State Museum to collect samples from multiple Onondaga sites. Those samples are in the process of being prepared for submission to the Center for Applied Isotope Studies (CAIS) at the University of Georgia the Centre for Isotope Research (CIO) at the University of Groningen. This work brings us very close to having all of the samples identified in our proposal collected.



New York State Museum

The team also presented the preliminary results of the project at the New York State Archaeological Association meetings. The paper contained some preliminary modelling from site sequences in Ontario and New York. Thus far the latest results are articulating very well with our pilot study. However, until we are confident that new dates will not alter those preliminary results we are not going to post them here. Altogether, the paper was met with a good response. The NYSAA meetings also gave us a chance to confer with other researchers who are interested in chronology-building in the northeast. Jim Bradley, an expert on Onondaga archaeology, helpfully offered to seek out samples from collections we were unaware of!

NYSAA meeting program

NYSAA meeting program

After the meetings, Jennifer Birch visited the archaeology collections at Syracuse University. Here, she was able to access collections from sites that were the basis of James A. Tuck’s research on the Onondaga for the project. This visit provided the opportunity to collect samples for the project as well as to examine some excellent examples of the “archaeology of archaeology” — in particular, the kinds of expedient containers artifacts may be stored in. In this case, cigar boxes and seed bags.

Syracuse University

Syracuse University

Finally, team members met at Cornell University for a day of updates and project planning before we all head off for summer fieldwork, dissertation research, and writing.

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A windy day on Cayuga Lake in Ithaca, NY

The sample collection phase of our project is very nearly complete and we are looking forward to submitting the final set of samples for phase I of the project. Expect great things in fall 2018 as the first sets of formal modelling and interpretation come together!

Dating Iroquoia at the NYSAAs

Our team will be presenting preliminary results of our project at the NYSAA meetings in Syracuse, NY on Sunday April 29. If you will be at the meetings, drop by and say hello.

Sunday April 29, 8:40 am, Jennifer Birch, Sturt Manning, Samantha Sanft, and Megan Conger. High-Precision Radiocarbon Chronology of Iroquoian Occupations in New York and Ontario: Preliminary Results and Implications.


Sample Collection in New York, at RMSC


The Rochester Museum and Science Center (RMSC) is the repository for about half of the assemblages from the New York sites in our project. Thanks to the amazing staff at RMSC, who approved our request to conduct radiocarbon dating and consistently facilitated our research, we have finished collecting all of our samples from RMSC.

Samantha, a research assistant with our Cornell team, has been traveling to Rochester over the last few months to collect data for radiocarbon sample selection. After piecing together information from site maps, RMSC site files, primary artifact files, and field notes, Samantha selected samples that will provide the most amount of information for our project. During subsequent visits, she assessed the condition of the samples and made sure that enough organic material from these specific contexts would remain in RMSC collections for future archaeological projects. Lastly, Samantha made one last round of visits to Rochester in order to collect the samples and bring them back to Cornell for further analysis. After which point, the samples will be sent off to the lab for radiocarbon dating!


It was incredible seeing the massive amount of organics recovered from some of the sites (see the gallon-sized bag full of carbonized beans from the Alhart site, pictured below) and it was fascinating learning more about how past peoples lived. The Alhart beans were recovered from a rectangular underground storage pit. The pit housed two bark barrels full of beans surrounded by corn cobs and contained a wooden ladle sitting on top of one of the barrels of beans – how cool!


Next, Samantha will travel to Albany to visit the New York State Museum.

Sample Selection and Submission, Round One

We have been busy preparing the first round of samples for submission to the Center for Applied Isotope Studies at the University of Georgia. These samples primarily consist of carbonized maize kernels and cob fragments from 12 ancestral Huron-Wendat sites in southern Ontario.

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Megan Conger preparing samples for submission to CAIS

Our project includes a multi-laboratory strategy to control for and ensure no inter-laboratory offsets. This means that we will be aware of how any differences in sample processing between the labs may be affecting the results.

For each site, at least one sample is being divided and split between two laboratories. This means literally splitting some carbonized maize kernels in half and dating each half separately. Overall, a mix of pairings will be used across three laboratories to establish that comparable results are achieved independent of the individual laboratories.

These samples will be joined soon by others from New York State in the first round of submissions. Once we have a sense of how the results from the first round are coming together, a second round of samples will be dated in order to clarify any ambiguities in the data set.

Sample Collection in Ontario, Round 1

Over the last few weeks, work on Dating Iroquoia really kicked off in earnest. Megan, a research assistant with our University of Georgia team, flew to Ontario to collect samples for our first round of radiocarbon dating, which we hope to submit before the end of the year. The sites we were sampling from were housed at 4 different facilities across the province: University of Waterloo (Waterloo), University of Toronto Mississauga (Mississauga), ASI Archaeological and Cultural Heritage Services (Toronto), and Sustainable Archaeology McMaster (Hamilton).

In all, we collected about 130 samples from 9 sites. This might sound like a lot of samples (and, to be fair, it is!) but we need to date many secure contexts from each site to really understand its internal chronology, which will then help us understand how the sites fit in time in relation to one another. We also collected a few more samples than we strictly need for the first round of dating, so that we have more samples on hand to date if we are able to.

The vast majority of the samples we brought home were carbonized maize kernels (Zea mays), although we also ended up with some maize cob fragments, some bramble seeds (Rubus sp.), a hawthorn seed (Crataegus sp.) and some beans (Phaseolus vulgaris). We mainly targeted the carbonized remains of short-lived plants, and here is why: we know that annual plants were only alive for a short period of time, which means that the time difference between the “oldest” carbon and “youngest” carbon in each kernel or seed is not very large. This reduces the chances that the carbon we end up dating represents the plant’s early life, rather than the time at which it was harvested and died.

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We also collected two other kinds of artifacts for radiocarbon dating: animal bone and charcoal.  These materials can provide dates that are just as precise as botanicals, but we have to be very careful in our selection of samples.  For animal bone, we had to make sure that we only sampled bone where we could absolutely identify the species of the animal it came from, and we couldn’t sample from any species that are aquatic, or which consume a lot of aquatic resources.  This is because of the marine radiocarbon reservoir effect,which traps older carbon 14 in deep water. This means that radiocarbon dates on organic material from aquatic species (like shell or fish) or species that consumed aquatic resources (like raccoons or some birds) require corrections, which aren’t part of our current research plan– although that would be an interesting and useful direction for future research!

For charcoal samples, we selected pieces of bark or chunks of charcoal that otherwise include the outermost rings of the tree, which formed closest to when the tree died.  Charcoal is a great material to use for radiocarbon dating, because it is often abundant on archaeological sites. But, because trees grow out in successive layers, there can be a difference of hundreds of years between dates taken from innermost and outermost rings of the same tree. We’re interested in when the tree died (and was presumably used by the people who felled it), so we were looking for those outermost layers.

This is just the first collection trip for the project. Samantha, the team’s Cornell-based research assistant, is travelling to the Rochester Museum and Science Center in Rochester, New York later this week on a sample selection scouting mission, and she’ll be collecting our first round of New York samples from that facility soon.

Dating Iroquoia: an overview

Between AD 1400 and 1600, societies of Iroquoian-speaking peoples living in what is now Southeastern Canada and the northeastern United States underwent profound changes. They built and lived in larger towns than they ever had before; they engaged in conflict with each other and with neighboring nations; they developed complex ways to cooperate and make decisions as a group; and they entered into the global economy.

Basically, people’s daily lives changed, massively.


Interior of a reconstructed Iroquoian longhouse. Photo: Wikimedia Commons

But when and how, exactly, did these changes occur? Did they happen gradually, bit-by-bit, at different times in different communities? Or all at once, spurred on by some geopolitical event or common cultural watershed? Did people of one generation live in the same kind of town that their parents did? Were they safer, with more social resources? Did they make a living the same way, and follow the same yearly rhythms as generations had before? These are the kinds of questions that archaeologists around the world wonder, but are generally not able to answer.  By combining existing archaeological data with new chronological models constructed using hundreds of new AMS radiocarbon dates, we are going to answer some of these questions, and rethink how we understand the historical development of fifteenth and sixteenth-century in Northeastern North America.

Over the past century, archaeologists have excavated dozens of Iroquoian villages in Ontario and New York. The artifacts, maps, and notes from these excavations are stored in museums and archives throughout the northeast. We’re going to choose samples of burned plants and bone from these sites and date them using AMS (Accelerator Mass Spectrometer) dating.  This isn’t new, of course—archaeologists have been using AMS dating for decades. What our project is going to do, though, is use those dates to create high-precision Bayesian chronological models (a process which we’ll explain in a later post). These models will tell us, with a high degree of certainty, when each particular site was occupied. This will then allow us to consider how those occupations relate to one another and to broader historical trends in the Iroquoian world.

Iroquoian sites are perfect for this kind of research because, for the most part, they were only occupied for a few decades. This means that we should be able to get a very precise understanding of when each site was founded, how long people lived there, and when it was abandoned, which will make it easier to put them in chronological order. Our goal is to date forty-two Iroquoian village sites, from six different areas in Southern Ontario and New York. Then, we’re going to use these new chronologies to reinterpret the trends we see in other kinds of archaeological data—tracking changes in the size and internal configuration of sites; in the amounts and kinds of European goods found on sites; in the evidence for conflict with neighbors and far-flung groups; which will help us develop new insights about the lived experience of social change in Iroquoian societies between AD 1400-1600.


Announcing “Dating Iroquoia”

Welcome! This is the official blog for Dating Iroquoia, an NSF-funded, collaborative research project between researchers at Cornell University and the University of Georgia. We’re going to use this space to share our progress on this multi-year, multi-institution project. We’ll keep you posted as we collect samples, send them off to the lab, construct models from them, and try to figure out what it all means. We’ll eventually collect all of the data and publications we produce here, too.

This post is just to launch the blog and website: expect periodic updates in the near future. In the meantime, check out the “About the Team” page to learn more about us, and the “About the Project” page to learn more about what we plan on doing.