Trace Evidence

That photo is from an early-1800s house upstate. There’s nothing exceptional about its structure, although architecturally and historically it’s interesting. But there are traces of the past in building materials, and it’s fun, and sometimes instructive, to take a look at them.

Here’s a marked-up version of the photo for reference:

The most obvious trace is at the red arrow: knob-and-tube electric wiring. It was first used in early electric installations in the 1880s, but this house was not wired that long ago. Knob and tube continued in use well into the 1900s. The house was wired some 80 or 100 years after it was built, but early enough that it got knob and tube rather than metal conduit.

The trace at the green arrow is pretty clear, too: the original plaster finish on the partitions was applied over wood lath. The thin white stripes are where there were gaps between the lath strips to allow the plaster to squeeze through and are simply gypsum stains on the wood.

The best trace is at the purple arrow. (It’s elsewhere, too, but most clear there.) It might help to zoom in a little to see it. There are a series of evenly spaced, parallel irregularities in the surface of the wood. Those marks answer the question of how this particular piece of lumber was cut from a log.

How do you get a rectangular wood beam or plank from a round tree trunk? All but one of the possible answers start in antiquity. You can use an axe to roughly cut the log into a rectangular cross-section and then use an adze to smooth the sides. That takes one person, two hand tools, heavy labor, and patience, but is otherwise foolproof. It is also recognizable because it leaves the surfaces of the wood with a series of faint scallops from the adze. You can use a pit saw, where the log is in a horizontal position and cut with a long saw in a more or less vertical position. One person pulls the saw up from above, one pulls it down from below. You can get the people and the log in position by using a hole in the ground – a pit – where the lower sawyer will work, or you can prop the log up on a set of sawhorses. This takes two people, a large saw, and the set up to make it work, but it’s faster than using an axe and adze. It leaves a set of slightly-diagonal imperfectly-spaced straight saw marks on the wood.

Powered saw mills go back to Roman times, using waterwheels and crank mechanisms to replicate the action of a pit saw. They were eventually improved by adding a mechanical conveyor that pushed the logs through the saw rather than requiring people to do that job. Once the conveyor was linked to the same power source as the saw, mills left a series of vertical, parallel, evenly-spaced saw marks on the wood. Another invention was the gang saw, replacing one blade with several, so that several pieces of lumber could be cut from a log at one time. The final critical change to the mill itself was the invention of the circular saw, which was less fragile than the long straight saws and used a much simpler linkage to the water wheels. The combination of a circular saw and conveyor, in addition to creating an indelible image from many early movies, left a series of evenly-spaced curved saw marks. Eventually, the waterwheels were replaced by steam engines and other forms of power.

So those evenly-spaced marks at right-angles to the long axis of the piece of wood tell us it was cut at a mill rather than by hand. Given the huge forests near this site and the 1820s construction date, that was not a given.