Dating historic timber
On the other hand, ancient wet sapwood samples seldom survive drying out.As a result, the sapwood should either be measured wet and then allowed to dry, or it should be frozen or kept wet.After cross-matching the chronology from the building with the chronology of living trees, it is immediately possible to figure out the dates at which the historic timbers used in construction were felled.Similarly, if an extended chronology is available, then dating of samples from buildings of known or unknown date is possible.This form of dating is the most accurate and precise absolute dating method available to archaeologists, as the last ring that grew is the first year the tree could have been incorporated into an archaeological structure.The utility of tree-ring dating in an environmental sense is the most applicable of the three in today's world.There are two types of dates that can be assigned to tree specimens: cutting dates, and noncutting dates.Which date is assigned to a specimen is dependent on whether or not there is evidence that the last ring present on the specimen was the last ring the tree grew before it died.
Not until 1998 was a Boston area master dating chronology developed.Even if a reference chronology is available, care must be taken to identify aberrations in the ring pattern to determine if the sample is usable for dating.Dendroarchaeology has been used extensively in the dating of historical buildings.The last step is to compare the rings with that of ring-width patterns in sampled timbers and a master dating chronology.For trees to be useful in archaeological analysis, they must "produce annual growth rings that are uniform around the tree stem", they must "live for decades and, preferably, centuries" and they "must have been used extensively by humans either for habitation or fuel." One of the problems with this evaluation is that it is possible under certain conditions for a tree to miss a growth-ring or produce two growth rings in a season.
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Once aligned, knowing the precise calendar year of any individual tree-ring is the same as knowing the calendar year of all the rings.