Replication of Delaminated Ft. Morgan Cemetery Headstones.
I am Alex Beard, I recently graduated from Xavier University in May of 2014 with a Bachelor of Fine Arts Degree with a Fiber Arts Concentration and a minor in Art History. I intend on going to graduate school to complete my Masters in Art Conservation. I am working at National Center for Preservation Technology and Training as a materials conservation research assistant under the supervision of Jason Church.
The project we have been working on this fall is the continuation and hopeful finalization of the Hard Water Effects on Granite.The origin and aim of this project were mentioned in my first blog post. My post today will discuss the replication and testing of the samples that has been underway in our laboratories.
After visiting cemeteries in the Western United States we attempted to replicate the conditions the granite headstones were subjected to and create our own test samples. Forty stone samples were cut to a manageable size of 1 5/8” diameter. Three different stones were selected for testing: Dakota Granite, Elberton Grey Granite, and Colorado Yule Marble. All three stone types used are native to the United States and are frequently used in the Ft. Morgan Cemetery. The granite types chosen were some of the victims of the most extreme cases of delamination in the cemetery. The white marble was chosen to act as a control of sorts; the marble headstones in the cemetery have not suffered the extent of scaling that the granite pieces have. 16 sample coins were cored out of the Elberton and Dakota Granites, and eight samples were cored out of the Colorado Yule Marble.
Once cut, half of each of the Elberton and Dakota Granite samples were polished using a series of coarse-to-fine (60 grit, 120 grit, 360 grit) grinding discs on a variable speed grinder-polisher. All of the marble samples were hand polished. The remainders of the granite samples were sandblasted. All of these samples were photographed, weighed, and their colors were collected and quantified using a colorimeter. Five Marbles, five sandblasted Dakota Granites (SDG), five polished Dakota Granites (PDG), five sandblasted Elberton Granites (SEG), and five polished Elberton Granites (PEG) had their surface profiles scanned and measured by a laser profilometer to quantify its roughness.
Four rows of ten holes were cut in a roughly 2’x 2′ square piece of heat resistant thermoplastic. The prepped samples were placed in the holes in a randomized pattern. We were now ready to reproduce the mineral scaling. Water was shipped to us from the Ft. Morgan Cemetery in Colorado in gallon jugs. This water was put in a holding tank with chiller lines running through it to keep the water’s temperature to 60 degrees Fahrenheit (the same temperature of cemetery’s well water). Four heat lamps were set up to direct even amounts of light and heat on the plastic test matrix with the sample stones. The temperatures of the water and stones were monitored and documented; thermal images were captured to ensure the lamps were evenly distributing heat. Once the stones had reached the optimum temperature, roughly, 120 degrees Fahrenheit, they were sprayed with the cooled Ft. Morgan water through mini spray heads (they were sprayed every minute and a half for three seconds). After several weeks, the stones developed a layer of hard water buildup, staining, and scaling.
After our “replication” Ft. Morgan cemetery stone samples were created we began quantifying the results. The stones were again photographed, massed, and their colors were measured with the colorimeter. These samples were also photographed using a microscope, scanned with a portable X-Ray Fluorescence analyzer to identify their elemental make-up, and their surface profiles were scanned using a laser profilometer.
We are confident that the cemetery’s irrigation system is the root of the hard water staining issue. The extreme fluctuation in temperatures between the well water and sunbaked granite caused the stone thermal shock, triggering micro-cracking. The constant expansion and contraction of the granite combined with the mineral rich water has hindered the longevity of the headstones.
Our next blog post on this granite project will be an update on the status of the cleaning tests. Can you suggest any chemical or mechanical cleaning methods for us to try?