nutguard Archives

DSCF0673 — Although the outside of the nut is degraded, the inside threads are easy to unscrew.

Hello Everyone! We’ve been busy in the turret for the last few weeks. As Kate explained in her post earlier, we are concentrating on removing the remaining nutguards. There are a total of 24 ringing the inside of the turret in various states of preservation. So far we’ve dismantled the smaller fragments and are working towards the larger, more intact ones. We chip away at the concretion behind the nutguards and along the edges until they can be lifted off. Some are still bolted in place and the bolts can be unscrewed with a wrench due to the excellent preservation of the inner thread system.

Once the nutguards are detached, we concentrate on removing the concretion that formed behind the barrier. This consists of hard iron corrosion and concretion mixed with sludgy sand and softer corrosion products. In addition to revealing more of the turret walls, we are interested in any remaining artifacts lodged behind the plates. Read more

Nutguard Part 2

June 9, 2010November 27, 2015

The nutguard discussed a few weeks ago has now been removed from its desalination bath. It was dried under a fan overnight then coated with a tannic acid solution to stabilize the surface. It was necessary to carefully scrape away numerous large flakes of rust from all over the surfaces of the object before the tannic acid could work. As the flakes came away bright metal was visible. The entire surface had an even black color once the tannic acid had been applied. A coat of acrylic lacquer was applied to give it some moisture protection and the object was photographed and placed on a padded mount for long term storage.

The most delicate part of the treatment was preserving a large iron fragment connected to the edge of the nutguard by just a tiny ribbon of metal. A cloth band on the storage mount secures it to prevent it from moving. Read more

USS Monitor Center

Nutguard Conservation Nearing Completion

February 26, 2010November 27, 2015

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 1/8^th 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.