NEWS Summary FOR CIVILWARNAVY.COM
Written by Joan Wenner
Recovered USS Monitor Dahlgren Gun Conservation
Newport News, Virginia—At the official repository of the artifacts of the recovered USS Monitor ironclad, The Mariners’ Museum & Park, the vessel’s port XI-inch Dahlgren gun is undergoing conservation efforts at the Museum’s Batten Conservation Complex indoor wet laboratory that opened in 2007. Conservation methods used to forestall oxidation and disintegration of the recovered gun involve containment and cleaning in a moisture-free environment containing as little oxygen as possible. Indoor large storage tanks hold the big, multi-ton artifacts like the Dahlgren guns, engine, condenser, and turret of the Monitor. Recovered iron objects are extremely unstable because they have taken on salt from the ocean; unless conserved, chloride from the salt will cause the metal to rust until it is virtually disintegrated, so the treatment helps remove the salt.
Dry ice blasting is a surface cleaning method that removes corrosion (from wrought iron, but not cast iron) without damaging the metal surface by firing a stream of dry ice at the surface with compressed air to physically remove salt in the corrosion itself, exposing the metal surface for other treatment solutions to more fully remove remaining corrosion. To clean the inside smoothbore of the cannon requires careful use of coring drills first, followed by removal of salts inside the bore.
The biggest challenge is compounded by their size and condition. Monitor’s Dahlgren guns weigh about 16,000 pounds each, and iron has corroded out of the surface layer, leaving a fragile layer of (mostly) carbon instead. With guns weighing 2,500 pounds or less and guns with a less fragile surface, drilling to clean the interior doesn’t need to be perfect. But with guns that are fragile like the Monitor’s Dahlgrens, normal drill methods are not feasible; there is so much weight on such a fragile surface that applying similar methods will gouge pieces out of the sides. Thus, brute force is not an option; the setup needs to allow alignment without applying force directly to the outside of the guns.
Once the Dahlgren guns are cleaned inside and out, they can finish desalination treatments until all salt is removed from the metal; subsequently, the guns are dried out in a controlled manner and protective coatings applied and the guns can be displayed in an environment with carefully controlled relative humidity. For further information on the conservation techniques, visit monitorcenter.org and select “Conservation” and “Blog” and view the conservation webcams. See also marinersmuseum.org.
For the complete news article with more details and photographs, see Joan Wenner. USS Monitor Dahlgren Gun Conservation Continues, Civil War News, Volume 44, No. 10, p 1, 3, October 2018.
Joan Wenner, J.D., is a longtime Civil War history writer and modern maritime writer. Her work has appeared in Civil War News, The Artilleryman, and in numerous boating and sailing publications.