This afternoon's visit to the site was primarily to meet another expert who has been brought in to help with the task of understanding Mingary Castle - Dr Coralie Mills, a dendrochronologist who is based in Edinburgh. She is here to do a preliminary survey of the wood that remains in the building, and to write a report which will outline the work she could do which will help in the archaeological investigations into the castle's history.
Dendrochronolgy is the science of dating wood by the variation in thickness of the annual growth rings in a tree. Good growing conditions during a summer produce wider rings than bad years, and the record has now been pushed back several thousand years.
When I arrived Coralie was looking at the three wooden steps in the north range, recently exposed by
Tom Addyman, which were part of the main staircase which led up from the front door to the upper floors. She was fairly certain that they were oak and that, although the central part of each plank was badly eroded, the sections sunk into the wall might provide enough tree rings of good enough quality to be dated.
To be able to carry out a dating, Coralie needs to be able to identify the species of tree that the wood came from, she needs a reasonable number of rings, a number of samples from the same phase of the building and, ideally, some of the sub-bark surface, the last ring formed before the tree was felled, which gives the earliest date when the wood could have been put into the building.
Earlier, she has been up into the original staircase, above, which was built into the east curtain wall of the castle. Here, wooden planks had been used to form a ceiling, and these were cut in a somewhat unusual and interesting way along the length of the tree trunk. All but one look to have been installed at the same time. There is a good chance of being able to date these and, since they are in an original part of the building, they might be very early.
I am most grateful to Coralie for the time she gave me to explain her work. She was looking forward to being involved with the archaeological exploration of this magnificent building, which she thought was the oldest she had ever worked on.
Hell Jon, thanks for that excellent summary of the dendro assessment visit and for taking time to meet up and write this piece. I'll be linking to it! Just to add to it briefly, after we met I counted another 42 or so historic timber elements surviving as lintels - quite remarkable really when you consider the site's exposure to the elements.
ReplyDeleteAnd on a more general point, the oak tree-ring coverage for Scotland is patchy geographically and chronologically, and we have only a continuous Scottish oak record for south west Scotland, which goes back into the 10th C AD, thanks largely to some early work on timbers from Glasgow Cathedral roof and other medieval sites by Prof Mike Baillie from Belfast(QUB)in the 1970s. He used the Scottish record to help bridge some tricky periods in the Irish oak record.
Thus Mingary could form a significant new piece in the Scottish tree-ring jigsaw puzzle, representing a far more north westerly oak site than any others dated so far, and if the material is as early as we hope, this will be a very important development indeed. We will have to see whether this material can be dated against the existing rather distant oak reference data, it may prove possible with sufficient sample replication (ie high sample numbers) and good sequence lengths (ie selecting samples with lots of rings) and the potential is looking good at this early stage, especially because, as you say, many samples appear to have sub-bark surface intact, good for getting precise felling dates to the year. Alternatively, building up a more local oak reference chronology - using long lived oaks - and other historic timbers - would be the way forward.
It was great to meet you and I'll be following your blog from now on, Mingary is now my favourite castle ever! Coralie