Cannon Conservation Project

The fortifications Castillo San Felipe del Morro and Castillo San Cristobal belong to the most important landmarks in San Juan, Puerto Rico. Besides their impressive appearance, and panoramic views of the coast and the San Juan Bay, they also house numerous cannons and artillery shells from the 18th and 19th centuries. While built with precision and attention to detail  to withstand the elements of warfare, the impact of time and nature was not considered in the manufacturing process. The cannons and other historical metal artifacts have been exposed to tropical and coastal climate conditions throughout the centuries, resulting in corrosion and leaving many objects in critical condition. 

In 2008 a first attempt was made to preserve the metal objects. A concept for a passive chemical chloride removal and a subsequent stabilization of all metallic artifacts was developed and treatments were started, but later discontinued. In 2014, a new project was launched in order to recover the artifacts, including UPRRP and NPS-SAJU as institutions and Cesar Pinero, conservator in private practice. Taking the previous treatment plan into consideration, an interdisciplinary approach to understand the dynamics of the cannon corrosion at El Morro and San Cristóbal was designed. Historical and material science research build the foundation needed to establish a timeline correlation procedure for the cannon’s manufacturing and materials science, as well as creating preservation guidelines and plans. 
Through physical-chemical analysis, the inner structural conditions of the artifacts are exposed and material surfaces during and after the treatment characterized. An electrochemical treatment and stabilization plan was developed to stop the corrosion processes  within the cannon tubes and artillery munitions shells and to stabilize the surface providing a realistic and pleasant visual appeal to the artifact. ​

Munition shells after conservation treatments

Photographic and written documentation of all measures form a crucial part of the projects, as well as the cataloging of all objects. ​

Students working on munition shells

Education and research outreach has been playing a major role within the project, and has been emphasized more and more throughout the years, providing university students with insights on conservation ethics and treatments.  The goal is to promote education and research experience in conservation science in Puerto Rico, as well as constantly reevaluate and improve implemented procedures and examination techniques. 
Out of a total of 24 cannons and approximately 500 artillery shells, four cast iron as well as 3 bronze cannons, and 175 artillery shells have been treated and are now back on display in the fortifications. Besides the electrochemical procedures, mechanical treatments are necessary to remove corrosion and concretions, requiring lots of helping hands. Numerous volunteers from the University of Puerto Rico, and NPS volunteer programs have contributed to the progress of the Cannon Conservation Program.

At the moment, four cannons and eighteen shells are being treated and are found in different stages of electrochemical and mechanical treatments. Students are assisting the conservators and NPS staff throughout the summer of 2019. 

For more information about past and current projects, contact us at:
​[email protected]
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