How Do You Feel About Humidity?

Frequent trips to the beach, firefly-lit walks around the oval, and stargazing on the back lawn: what’s not to love about summer at Stratford Hall? I can think of only one thing – humidity. I hate humidity, and anyone who has spent time on the East Coast knows we have a lot of it. Sometimes when the humidity climbs to 80 or 90%, I feel like the air is giving me a big, sticky, inescapable, and unwanted hug. General unpleasantness aside, there is another reason why I strongly dislike humidity. It can wreak havoc on museum collections.

Now just to clarify, when we talk about humidity, we actually mean relative humidity (RH), which is the amount of water vapor contained in air at any particular temperature. RH in itself is not a bad thing. However if it is too low, too high, or fluctuates too much, it can cause objects to shrink, swell, crack, split, and warp. Incorrect RH can also cause a host of other nasty problems, such as mold and the corrosion of metals.

So as you can imagine, Stratford Hall closely monitors humidity levels in collection areas. Scattered throughout the Great House and the Visitor Center galleries are nine HOBO data loggers that record, on the hour, the temperature and RH. See if you can find them the next time you’re at Stratford. Be prepared! They are hidden pretty well.

As the collection management intern, it was my job to analyze the data from the HOBOs (it’s more interesting than it sounds, I promise!), and I am proud to report that for the most part things are looking pretty good! Take the Paleo case, the display case with the shark’s teeth in the Visitor Center, for example.  Most conservators recommend 70º F and 50% RH +  5 as ideal conditions for most collections. When you look at the included graph, you can see that the temperature and RH in the Paleo case are almost spot on.  There is still a bit of fluctuation, but not enough for us to worry about. These fluctuations were probably caused by the opening and closing of the Visitor Center’s door or the presence of moisture-exhaling visitors. That’s not to say Stratford Hall doesn’t have some issues with humidity. Every collection does.

If you’ve recently been in the Southwest Outbuilding, you may have noticed an empty display case on the exhibit panel in the carpenter’s shop. Even though the Southwest Outbuilding is climate controlled, it occasionally experiences high and fluctuating RH. The occasional day of high RH was enough to cause a Lee era nail to corrode and break in half. The nail has been sent to conservation, and the display case is being retrofitted with silica gel so the collection manager Karen can better regulate the RH.

This summer I also tackled mold, another byproduct of high RH. Recently, mold developed on a table in the kitchen outbuilding (the kitchen is not climate controlled). Luckily, removing the mold was relatively easy. Karen and I let the table air dry and then vacuumed up the spores and wiped the table down with alcohol. We can prevent future mold growth by installing a dehumidifier in the kitchen.

Although I dislike humidity, I enjoy keeping track of it because monitoring RH allows museums to decrease RH-related deterioration like the examples above. Then again, maybe I just like making graphs.

Check out this link for more info:

-Mollie Armstrong, Collections Management Intern