How it's done: Stages 4-6
Stage 4: Licencing for altering & exporting bone samples
When sampling a bone for the various tests we need, it is necessary to remove part of the bone and crush it. Therefore, the bone will have a small part of it missing when the research is complete – the method is destructive but necessary.
Because of this, the pack need permission from relevant authorities to alter (i.e. remove a piece of) the bone and a second licence to export that sample to the lab for testing.
We cannot proceed without these licences and these permissions are to safe-guard and protect finite and limited recovered archaeological bones from various sites.
In Ireland, it's the National Museum of Ireland that grants the licences.
Stage 5: Sampling the bones
After we obtain the licences, three different samples will be taken from each individual dog or individual bones from the sites. Each sample/bone is wrapped up carefully in tin-foil, placed in a small zip-lock bag containing a label with a code and this code is also written on the bag. The bags are wrapped in protective bubble wrap, a list printed (and emailed) with contents and are boxed ready for posting.
Only a small amount, 1g (equivalent to the weight of a metal paper clip), is required for stable isotopic analysis to send to Darren in Durham University, UK or Brian in University of New Brunswick, Canada.
We send either a tooth with a root or the ear bone (petrosal bone) to Pontus at The Francis Crick Institute, UK so he may extract ancient DNA from its centre. There will be left over fragments of the tooth or ear bone from this analysis.
Another 1g sample is required for radiocarbon dating at 14CHRONO radiocarbon dating laboratory in Queen's University Belfast, Northern Ireland, where Gerard will look after all the samples and get them ready for radiocarbon dating.
Stage 6: Radiocarbon dating
Gerard at 14CHRONO will date our dog samples – they are in safe paws!
Each bone sample has a code assigned to them (UBA-XXXXX). We can cross-reference our dog details with each UBA coded sample. Once each bone sample is reduced to powder it is treated with chemicals to clean and remove any contamination from the ground. Collagen, a protein found in bones, is extracted from the sample. This is the best for dating.
Next, we need to get the carbon dioxide from the sample. To do this, we burn 0.0003g of our collagen. The carbon dioxide gas is captured and transformed into solid carbon – graphite! Just like you find in your pencils!
Each graphite sample is pressed into a small aluminium target. The targets are lined up 40 at a time to go into the AMS (Accelerator Mass Spectrometer). The AMS is a particle accelerator. It separates the different isotopes of carbon so we can count them. These numbers are used to give us a raw radiocarbon date.
Finally, when all the radiocarbon dates are gathered. a special kind of statistical analysis called Bayesian analysis is carried out to further refine and interpret the results. Then we calibrate these dates to a calibration curve to offset the effects of past atmospheric changes. This is because the amount of radiocarbon (14C) in the atmosphere isn’t constant i.e. it varies over time. The results must be converted to calendar age equivalents using a calibration curve which compensates for these fluctuations in atmospheric 14C concentration. We use a IntCal20 – the Northern Hemisphere Radiocarbon Age Calibration Curve. This gives us more accurate results and confidence in our age results.
While Gerard works away in the lab, we play the waiting game and go on lots of walks with our dog companions and try not to ask Gerard too many times, "Are they ready yet?"! It will take a few months before we get all our dating results back.