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November 04, 2015

Infrequently Asked Questions: How does one clean the Liberty Bell?

The world is full of questions we all want answers to but are either too embarrassed, time-crunched or intimidated to actually ask. In the spirit of that shared experience, we've embarked on a journey to answer all of the questions that burn in the minds of Philadelphians -- everything from universal curiosities (Can rice really fix a water-damaged phone?) to Philly-specific musings (Why do avenues like Passyunk run diagonally?). 


There are few -- if any -- treasures in Philadelphia as precious as the Liberty Bell. And like any valued antiquity (but especially one that's 264 years old), it surely needs a good wipe-down every now and then. 

So, how do they clean it?

In search of an answer, we reached out to Independence National Historical Park Curator Bob Giannini, who's been caring for the Liberty Bell since 1971.

How do you clean the Liberty Bell?

We don’t really do too much to it anymore. There was a time when we used what we call a Renaissance micro-crystalline wax up inside the bell, not on the exterior but on the interior surface. And the reason we were doing that is because back in the early 1980s we noticed a powder that was forming in the interior of the bell. At that time, we had a number of folks who came and helped us determine what it was. It turned out it was something called ammonium sulfate that had been actually causing this powdery substance to appear on the interior of the bell. But mainly we got in touch with folks from the Philadelphia Museum of Art and their metals conservators and metals conservators from the National Park Service, and the DuPont chemical company, and worked with those folks to figure out how we should best approach the problem with the bell. And so Andrew Lins, who’s a metals conservator at the Museum of Art, brought a team over in the mid- to late- 1980s and they cleaned the entire interior surface of the bell off. Then they treated it with Renaissance micro-crystalline wax. And we also used a hard carnauba wax to cover that up once the process was finished.

We sort of just keep an eye on it from year to year. There was a point in time where we did [the treatment] on an annual basis. But it was about three months ago that Andrew came with his crew and took a look at the bell, and they said they think we don’t need to do it as often. So we’re following his instructions now, more than anything else.

What does the Renaissance wax do?

It prevents the stuff from getting to the metal of the bell. The bell’s metal. It’s the bare surface you have to worry about. And so what the ammonium sulfate -- if it gets into the metal it can cause problems. And that’s what we were seeing ...

How often do you clean the bell?

We were cleaning it twice a year, but now we’re down to once every year, or two years. It’s in pretty good shape; we’ve got it looking good. It’s well protected right now. We know what to look for as far as this ammonia byproduct attacking the bell -- it’s no longer there, to the best of our knowledge. But you know, the bell can receive ammonia just from people’s hands, from perspiration. And that’s one thing. But we’re not sure, even to this day, how that started. It could have been from fertilizers used in the garden outside of the old Liberty Bell pavilion back in the 1980s. Or also, it could have been from – I know our custodial people who cleaned the windows inside of that pavilion in the ‘80s, they were using ammonia Windex spray to clean the windows. And it could be a possibility that a rag may have had some ammonia on it and someone inadvertently tapped the bell with it. But we do not know. We absolutely do not know how it came about. There are a lot of theories and things like that, but we were never able to pinpoint the exact cause of the problem. But it seems it’s under control now and we’ll ask Andrew and his staff to come back as needed and we’ll go from there.

Do you need any kind of special application tool for cleaning it?

No, not really. You have to warm the wax up a bit, and apply it, then rub it in. It’s almost like polishing your car.

Do you ever get nervous when you’re rubbing it?

[Laughs] No, no. It’s a pretty solid piece of metal …

What would happen if we didn’t have any preservation efforts?

Then you would run into some problems if [ammonium sulfate] got up into the bell itself. The bell is -- I don’t know if people realize this -- but the way it was manufactured back in the 18th century, it’s extremely porous inside the metal. And if you had portions of it where the [ammonium sulfate] gets into the cavities you could have a major problem. But that doesn’t seem to be the case. We do have it under control. I’m sure of that. We have good people from the Museum of Art, and their metals experts are unbelievably good.

Will there ever be a point when the metal deteriorates to where it’s no longer a bell?

I don’t think so. I mean, who could say? How long are we going to be here? As long as I’m here and I think the next couple generations, there should be no problem with the bell. It’s in safe hands.

Any little-known facts about the Liberty Bell and taking care of it?

One of the things the park service prides itself in is we always looked at it as conservation is preservation. We’re very mind-conscious of preservation and preserving our antiquities. The Liberty Bell is one of those things and, as far as I’m concerned, being that I work at National Independence Historical Park and take care of the bell, it’s the most important icon we have in American culture today. I know we have some competition with the Statue of Liberty, but I still consider the Liberty Bell -- it’s so small, but an extremely sacred and venerated object.


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