The Effects of Acid Rain on Monuments

May 28, 2012

Next time you’re visiting Mount Auburn, take a walk through the oldest parts of the Cemetery and you’ll notice a trend.  Almost every monument in these areas is made of white marble.  Marble was the stone of choice during the Victorian era and was widely used for both its beauty and ease with which sculptors could carve it.  Yet, there were drawbacks to using a stone like this.  In the monument trade, marble was an expensive material to use and the best quality marble usually had to be imported from Italy.  Unfortunately, the qualities that cause marble to be loved by sculptors also make the material more vulnerable to the freeze and thaw of New England winters and to a phenomenon that began to be observed during the Industrial Revolution – acid rain.

Pure water has a pH level of 7.0, meaning it is neutral.  Currently, the pH level for ‘normal’ rainwater is around 5.7, technically making rainwater acidic.  Some of this acidity occurs naturally, but most of it occurs due to manmade conditions.  When rainwater has an acidic pH level, a reaction occurs that forms carbonic acid.  Most of the acid in rainwater is a result of this reaction.  Acid rain has such a detrimental effect on the degradation of marble and other building materials (like limestone) because these stones are composed primarily of calcium carbonate, a mineral that dissolves when it comes in contact with acid.  To put all of this into perspective, human industrial activity over the past century has increased the acidity in rainwater to, in some cases, 1000 times more acidic than normal levels!

If the problem of acid rain began over a century ago, why did the Cemetery continue to allow the use of marble monuments that would not fare well under these conditions?  Our archives show that marble monuments were still far too popular to outright ban; however, we do have records that indicate that the Cemetery’s Superintendent often wrote to families in the hope of dissuading them from choosing marble monuments.  In these cases, granite was often suggested as a suitable replacement.  Eventually, the use of marble monuments waned across the country as granite became the new stone of choice.  This change in tastes can be seen by walking through areas of the Cemetery that were developed after the Victorian era ended.

If you closely examine any one of the thousands of marble monuments found at Mount Auburn, you will find that each one of them is slowly disintegrating in some way. The signs of damage from acid rain can be seen in illegible inscriptions or in the wearing away of intricately carved details that are found on many of the Cemetery’s most treasured monuments.  As for the marble monuments that are under Mount Auburn’s care, there is nothing that that can be done to stop the irreversible damage that acid rain has and will continue to cause. But efforts are being made to slow down the effects of the acid rain.  There are treatments that can be used to help slow degradation and, during the winter, special covers are used to protect some of the Cemetery’s priceless works of art.  Unfortunately, not every monument is able to receive this kind of special attention.  But there is a way that you can help!

Mount Auburn is always looking for volunteers to join its Monument Inscription Program.  This program uses special techniques to document as many monument inscriptions as possible before they are lost forever.  If you are interested in joining the Monument Inscription Program or would like more information about it, please contact Jessica Bussmann.

 

 

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