Monitor’s two gun carriages are the focus of a new disassembly project. The gun carriages are composed of copper alloys, wrought iron and wood. The iron and copper components are in contact, which causes galvanic corrosion. Contact between metals of different nobility will generate, over time, the protection of the more noble metal to the detriment of the less noble metal. Additionally, sea water acted as an electrolyte for reactions between the different metals for over 140 years (while salts found their way into the most remote places in the metallic matrix). Dismantling these objects will slow the iron corrosion process and increase the desalination rate of all components, regardless of material type. Of major concern is the removal of wooden carriage components in order to clean and treat them separately since they require different attention than metals.
The carriages have been stabilized since 2004 with an impressed current system in tap water. Conservators were reluctant to place the object in a high pH electrolytic reduction treatment due to the presence of organic components that would be harmed by the harsh alkaline solution.
In 2009, the conservation department rotated both gun carriages to their original upright orientation thanks to the magic of Gary Paden, who designed and built custom rotation rigs (see Nov 2009 blog). Having the objects right side up allows better access to many areas of the carriage, thereby facilitating easier disassembly. That was the idea behind the rotation.
This week, disassembly of the port carriage commenced and we made great progress! The four face-plates of the side frames were removed along with the 84 screws that were fastened the plates to the wood (88 copper alloy parts down!). The following pictures show Gary removing a face-plate.
These pictures make the work look easy but we had to fight the screws that were very, very tightly fastened to the wood underneath, not to mention that sometimes the screw heads had been corroded with time and worn by use during the Monitor’s lifetime. So, sometimes dismantling involved tapping screws in order to remove them.
A dozen side bracket bolts were also removed. These wrought iron bolts secured thin iron plates to the wood carriage frames. Here again, these things are pretty “stuck” and removing them is a workout. There are still 56 bolts to remove before freeing the wood elements… we’ll get there!
Today, the port cap square, another significant copper alloy element, was successfully disassembled from the carriage and placed in its own desalination and treatment container. Below, the picture shows one of the wrought iron bolts that secured the cap square ready to be placed in a fresh sodium hydroxide bath.
Finally, here are some overall pictures taken yesterday morning. The wood components have a beautiful rust color that will ultimately be removed during treatment. The copper alloy face plates of each side frame were covering them for the last 148 years, until this week! Enjoy!