MAG-C63: a tree-ring standard for AD 1586
Dr Alex Bayliss1, Dr Michael Dee, Mr Robert Howard, Dr Daniel Miles, Mrs Cathy Tyers, Dr Lukas Wacker
1Historic England, , United Kingdom
Standard materials are fundamental for accurate radiocarbon dating, but must be available in sufficient quantities for all AMS facilities worldwide to use as required.
MAG-C63 is a beam removed from the Great Tower at St Mary Magdalen College, Oxford during repair works in the 1960s. It is 20 feet long, by 12 inches square and weighs over a metric tonne. It has been securely dated by ring-width dendrochronology as spanning AD 1480-1609, and has been purchased in its entirety by Historic England.
The ring selected for use as a tree-ring standard is that for AD 1586. It is 2.76mm in diameter, and sufficiently close to the outside of the timber that dissection in quantity is feasible, yet far enough from the outside of the timber to minimise the potential for contamination.
Whole rings (earlywood and latewood) have been dissected by professional dendrochronologists, each sample being split across the ring so that it contains approximately equal amounts of earlywood and latewood. Each sample weighs approximately 50mg.
We estimate that MAG-C63 will supply 40,000 such samples. These will be made available to the community on a cost-recovery basis by Historic England over the coming years.
Alex Bayliss is Head of Scientific Dating at Historic England. She has used of Bayesian statistics for chronological modelling in archaeology routinely for over 25 years, constructing hundreds of models from thousands of radiocarbon dates. She is a member of the IntCal working group, and is currently developing the use of radiocarbon dating to inform the conservation and repair of the historic buildings.