The 1776 Keedy House on Barnes Road north of Boonsboro, MD

QUIZ: What do Mount Vernon and the Tower of London have in common with the following Washington County historic homes??

Keedy House, Boonsboro, MD

Middlekauff-Poffenberger Farm, Sharpsburg, MD

Mary Locher’s cabin, Antietam National Battlefield, Sharpsburg, MD

Joseph Poffenberger Barn, Sharpsburg, MD

Roulette House, Sharpsburg, MD

Roulette Barn, Antietam National Battlefield, Sharpsburg, MD

One of two period homes on the Middlekauff-Poffenberger (Kelly’s Purchase) on the east side of the Sharpsburg Pike north of the Antietam National Battlefield.

ANSWER:  Dendrochronology 

Washington County is blessed with some amazing structures. Sadly, not every builder inserts a date tablet. All the above listed structures were dated by dendrochronology, or tree-ring dating, the scientific method of dating based on the analysis of patterns of tree rings, also known as growth rings. Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year.

The technologically-advanced service was preformed by the Oxford Tree Ring Laboratory, 25 E. Baltimore Street, Baltimore, MD., proprietors Michael Worthington and Jane Seiters. To read the detailed information of this company’s research on Washington County and other Maryland structures visit their website at dendrochronology.net.

The way dendrochronology works is relatively simple. As a tree grows, it puts on a new growth or tree-ring every year, just under the bark. Trees grow, and put on tree-rings, at different rates according to the weather in any given year: a wider ring in a favourable year and a narrower ring in an unfavourable year. Thus, over a long period of time (say 60 years or more) there will be a corresponding sequence of tree-rings giving a pattern of wider and narrower rings which reflect droughts, cold summers, etc. In effect, the span of years during which a tree has lived will be represented by a unique fingerprint, which can be detected in other geographically-similar tree-ring chronologies.

Dendrochronological drill

To obtain this fingerprint, a radial section of timber from the pith or centre of the tree out to the bark edge is required . Once prepared, they are then measured under a  microscope using a traveling stage electronically displaying displacement to a precision of 0.01mm. Each ring or year is represented by its measurement which is arranged as a series of ring-width indices within a data set, with the earliest ring being placed at the beginning of the series, and the latest or outermost ring concluding the data set.

For those who simply must read-all-about-it, the following dissertation is available on-line with some excellent references to the Maryland sites.

http://tigerprints.clemson.edu/cgi/viewcontent.cgi?article=2374&context=all_theses

Roulette Farm, late 18th-mid 19th century, Sharpsburg, MD