Nutguard Conservation Nearing Completion

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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.

Silver or Not Silver?

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A beautifully preserved manometer was found attached to the engine. The gauge, which measures temperature and pressure, is currently under treatment. It has been dismantled as much as possible to assure better removal of the chlorides (e.g. the “conservators’ nightmare”). The main body of the gauge is made of copper alloy, and two wood stoppers enclose the top and bottom. The wood pieces are firmly embedded in the gauge and will therefore be treated intact and in contact with the copper alloy body. Former conservators carefully removed the mercury still in the glass component (see x-ray below), after which the glass part was separated from the gauge. This element is now fully conserved.

The scales were also separated from the gauge body and are currently being cleaned. They particularly attracted our attention because they seemed to be made of a silver alloy. However, the aspect of the corrosion products covering them was uncommon and the response of the metal to chemical cleaning tests was not what conservators expected from a silver artifact. Prior spot tests to identify the alloy were contradictory so it was decided to send one of the scales for an X-ray fluorescence analysis (non-destructive method) at the Northrop Grumman shipyard in Newport News. This silvered surface appeared to be a nickel alloy named nickel-silver or German silver. This alloy was mainly used due to its hardness and resistance to corrosion. Considering that 150ºF could easily be reached in the machines room, it makes sense that this alloy was used on a tool that needed to be readable at any time. Neat story!

What’s New with the Coat?

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As with many artifacts, finding the most suitable treatments for the wool coat involved exploring a lot of options. Ten cleaning methods and thirteen consolidation/drying techniques were tested and assessed on samples of the coat.  Quite a lot of work, but now we have them identified. These methods will properly conserve the artifact, be reversible, safe, and inexpensive. 🙂

The coat is getting cleaner and will be ready to dry sometime soon!

Turret Core Sample

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A while ago, conservators, archaeologists, shipyard employees, and a corrosion expert removed a core sample from Monitor‘s revolving gun turret armor. Although long-term analysis is ongoing, yesterday we utilized a portable XRF analyzer to perform additional elemental analysis. We’ll let you know what our results are after we have a chance to review them. In the meantime, check out this picture. The 2″ metal disc is a section of the turret’s iron armor plating. It is resting on the XRF analyzer.