Frizzled Fates: Tales of Humidity, Hair, and Collections Management

For our Collections Managers, humidity is the enemy (well, one of many). As someone who works with a group of talented people at HAI, I was fascinated to learn more about the instruments that measure humidity and how it overlaps with the human body.

First, a crash course on humidity and collections. Humidity measures the amount of water vapor in the air we breathe. For collections, we are really focused on the relative humidity – this is measuring water vapor in terms of how much exists in air at a certain temperature compared to how much water vapor can possibly exist in the air at that temperature. For example, for those in our Rockville office, you know that warmer temperatures can hold more water vapor – and thus you get a delightful swampy heat that you can swim through in the summer.

While humidity can be unpleasant for us, it can wreak havoc on our historical objects and records. In collections with multiple formats, wild fluctuations in temperature and relative humidity can lead to all sorts of damage. I recently worked on a project involving wet tissue samples. If environmental conditions change, it can lead to disaster for the specimen. If temperatures are too high, the specimens could deteriorate, and the preservatives could evaporate. On the flip side, low temperatures could cause solidification of certain organic matter.

So how do we monitor collections for change?

Saussure’s hygrometer

Saussure’s hygrometer

There are different tools that we use, but the ones I am most fascinated with are the hygrothermograph and hygrometer. It measures humidity with human hair. Why, you ask? It turns out that hair is dependable in its rate of change – humidity goes up and strands lengthen, and contract or shrink when humidity goes down. John William Draper’s A Textbook in Chemistry (1861) features Saussure’s hygrometer. Draper wrote, “It consists of a human hair eight or ten inches long… fastened at one extremity to a screw… and at the other passing over a pulley… being strained tight by a silk thread and weight.”

This hygrometer (modeled after one invented by Jean-André Deluc) is made from whalebone.

This hygrometer (modeled after one invented by Jean-André Deluc) is made from whalebone.

A Swiss physicist, Horace Bénédict de Saussure, invented the first working hygrometer in 1783 (though Leonardo da Vinci created a crude one as far back as 1480). His hygrometer—a hair tension hygrometer—has evolved and is still in use today, with a whole host of other electronic (non-hair) options. But all manner of objects were used over in these devices over the years, including an oat grain husk and ox gut.

Today’s Collections Managers likely have a digital hygrometer (which you can find in your local hardware store) – we’re not all carrying hair tension hygrometers around. But there’s something to be said for human ingenuity in creating such a device. History and science are weird and wonderful.

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Stephanie Webster

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