SAN JUAN, Puerto Rico, June 30, 2010 -- A Siemens high-purity water treatment system at the San Juan National Historic Site in Puerto Rico is helping to conserve valuable artifacts that are part of magnificent fortifications built by Spanish troops beginning in 1539. The historic site includes the Castillo San Cristobal, Castillo San Felipe del Morro (“El Morro”) and Fort San Juan de la Cruz (El Canuelo), the San Juan Gate and most of the city wall. These defensive fortifications surround the old, colonial part of San Juan, and are now part of the historic site, which is a unit of the National Park Service.
A reverse osmosis (RO) system from Siemens Water Technologies is providing high-purity water for conservation efforts. The 0.4-gallons-per-minute RO system (Vantage System, model M21R000), pretreated with softened water, is installed at the Santa Elena Guardhouse, a structure that was built in the second half of the 19th century and is located on the grounds of El Morro. A fenced area in the building houses several cannons and artillery shells that are being treated with this high-purity water.
“The water is used in the last phase that the cannons and shells receive as part of their treatment,” says Javier Martinez, Archive Technician for San Juan National Historic Site. “The goal of the treatment is to have the lowest perceptible amount of chlorides in the solution. Regular tap water contains chlorides, whereas RO product water has none. We use a combination of RO product water and high alkaline chemicals and the strong base sodium hydroxide to remove most of the chlorides that remain in the artifacts.”
Metal objects, especially those made of iron, are very susceptible to corrosion from chloride, which is found in high concentrations in sea water. The artifacts’ proximity to the ocean contributed to their corrosion. Chlorides can be removed from metal objects by electrolysis, during which the objects are immersed in a solution of sodium carbonate and RO water. This solution works as an electrolyte and corrosion inhibitor because of its elevated pH. During electrolysis, chlorides are drawn away from the metal object and into the electrolyte solution. Reverse osmosis removes 90-95% of the chloride from water because of its ability to reject salts in a solution.
The restoration effort is a cooperative agreement between San Juan National Historic Site and the Conservation Research Laboratory at Texas A&M University, which is part of the Center for Maritime Archaeology and Conservation. The cannons have been exposed to the harsh environmental conditions of Old San Juan as well as the impact from visitors. Every year, a half million people use the 23-acre grassy area on the grounds of El Morro for picnics, sports and other activities. The level of deterioration was so bad that invasive conservation methods were needed.
Says Martinez, “We requested water system quotations from different water treatment companies in Puerto Rico. This information was evaluated by the lead project person from Texas A&M. He determined that the Siemens equipment met the standards for quality and amount of water needed. Also, the Conservation Research Lab uses Siemens equipment, and the lab personnel recommended Siemens to us.”
By soaking the artifacts for six months in a solution of RO product water and alkaline chemicals, Martinez is assured that the least possible quantity of chlorides remains in contact with the metal before the stabilized artifacts are returned to the exhibits.
So far, the system has operated reliably and is producing the quality and amount of water required. “These forts are the biggest attraction in Puerto Rico,” says Martinez, “and by conserving their artifacts, we ensure that they will be around in the future for visitors to enjoy.”
