Dendrochronology Analysis Fails to Pinpoint Exact Dates of TLH Building Campaigns
We know from documentary evidence brought to light by Sandra Rux’s history that the TLH was initially built sometime between 1731 and 1738. A gaggle of old house detectives — looking at architectural styles, wood trim molding profiles, construction methods, surviving hardware, and old nails — date the expansion of the house more speculatively to the 1760’s. To nail down those dates scientifically, we contracted dendrochronolgist Bill Flynt to come to the house and practice his art.
Dendrochronology is the science of dating wood material, typically architectural timbers, to a specific year by analyzing the pattern of tree rings, or the annual growth rings within a tree trunk. A usable sample is a piece of wood (lumber, framing, etc.) that contains a bit of bark or goes to the edge of the bark so that the full growth history can be ascertained. The samples are then analyzed microscopically and compared to a database of other samples taken in the region that have been linked to a date certain. Thus, for example, you take a good sample of northern white pine from a joist under the attic floor in a Portsmouth colonial house, decipher the tree ring pattern under a microscope, then look for a match for that pattern in other samples of that wood in the region that have been dated.
Having been through this process before many times and intimately familiar with the house, TLH project manager John Schnitlzer prepared the way for Bill Flynt by identifying wood elements that would be good candidates for dendro analysis. He found what he thought was a good number of candidates. When Bill Flynt came by in January to take his samples, he agreed. The prospects for getting some specific dates for the house looked promising. We were hoping for a conclusion that might read: “dendro analysis shows that the house was likely built in 1733 from timber felled in 1732, and expanded to its current size between 1764 and 1766, as evidenced by several framing elements from trees felled in 1763 and 1764.”
Back in Bill’s lab – or, rather, inside his computer – in Dummerston, Vermont, however, our dendro dating hopes were dashed. The samples taken were good –getting to the edge of the bark – but there was insufficient material in the existing dendro database to match to a previously dated sample. In other words, looking at a sample of northern white pine from the TLH, there was nothing in the database from samples taken in the region – say, coastal New England from Newburyport, Massachusetts to York, Maine, and inland from there — to match to our sample. Bill’s dendro report, with its frustrating struggle to find a match for TLH samples that included white pine, hemlock and spruce, is posted on this website.
Not all is lost, however. If and when the database of existing dendro samples in the region — say, coastal New Hampshire and inland, from where timber would have been sourced — is expanded, the TLH dendro samples can be re-examined. So New Hampshire, and Portsmouth, New Hampshire, in particular, needs more dendro. To that end, John Schnitzler and Sandra Rux, two stalwart students of the TLH and of 18th-century buildings in Portsmouth in general, are looking for ways to build up the New Hampshire dendro database. Sandra Rux says the idea is to persuade several house museums with good documentation on the ages of their properties to participate. These include the usual suspects — the Warner House (built 1716-1718), the Moffat-Ladd House (1760), the Wentworth-Gardner House (1760-1762) and the John Paul Jones House (1757-58) – but there are other candidates as well, Sandra says. Grant money would help pave the way.