Inside the Monitor’s turret there are a series of thin wrought iron plates that covered the rows of nuts and bolts that held together the turret armor. The purpose of these plates was to prevent the nuts from breaking off of the bolts and flying around inside the turret when the armor took a hard hit during battle. The plates, known as nut guards, were about 1/8th inch thick rolled iron sheets, a couple of feet wide and several feet long, with the sides curved like a deep cookie sheet. Each nut guard was held in place by a pair of bolts near the top and bottom edges of the plate. The spaces behind the nut guards filled up with muddy sediment while the Monitor was sitting on the bottom of the ocean.
Recently one of the nut guards was removed from the turret so that the sediment could be carefully removed. The plate was then isolated in a small treatment tank where it underwent desalination. The nut guard did not fare well in the ocean because the plate is made of relatively thin wrought iron sheet. Numerous holes have rusted through the sheet and the curved edges are very fragile. It has been soaking in a pH 12 sodium hydroxide (NaOH) solution while undergoing mild electrolytic reduction. The chloride level extracted into the solution has been stable for several weeks. On Tuesday we changed the solution one last time. We also washed away quite a bit of soft surface rust and corrosion flakes in the process. The surface looks surprisingly good after having spent a hundred and forty years on the bottom of the ocean. Conservators are now soaking the artifact for about two more weeks prior to rinsing the artifact to remove residual sodium hydroxide. The artifact will then be removed from its rinse and then dried. The next challenge is to create a supportive mount to store and display this heavy but very fragile artifact.