Dahlgren Gun Tools: an In-Depth Look at Treatment, Part II

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In this blog post we’ll continue the discussion about one of USS Monitor’s gun cleaning tools, and the conservation treatment it has undergone.

Review

Image of gun tool before treatment.

In Part I, I discussed the purpose of the gun tool. I also showed how the way the gun tool was constructed made it impossible for me to disassemble the tool and treat the metal and wooden parts separately. This meant I was going to have to think outside the normal conservation treatment box and treat the wood and metal parts together. I also mentioned that I found textile wrapped around the iron handle and that I’d have to take extra steps to ensure it was preserved through treatment. 

Preserving the Textile

Detail of textile wrapped around iron handle.

First, I spent time finishing the cleaning process, to ensure the textile and other surfaces had as much dirt removed as possible. Once the textile was fully cleaned, I decided to coat it with a waxy consolidant. The wax coating would support the textile through any further treatment and protect it from abrasive damage. The best part is that the wax coating can be easily removed at the end of treatment. 

Gun tool after waxy consolidant was applied to textile

Removing the Salts

If you read conservation blog posts often, you may already be familiar with the fact that salts can be a major cause of degradation and decay in archaeological objects. At Mariners’ we often use a process called electrolytic reduction (ER) to help remove excess salts from the USS Monitor objects. Monitor objects absorbed significant levels of salt after the sinking, and so we can’t dry the object until salts are removed. 

A 9-inch shell showing degradation due to salts

With metal objects, we are able to use ER to speed up salt removal. However, because ER usually occurs in a very basic solution, it is hugely damaging to wood and other organics. So standard Electrolytic Reduction wasn’t an option for the gun tool. However, research and talking to colleagues led me to try a method of ER using a neutral solution instead of a basic one. Using a neutral solution means that it is safe for the wood and textile, but the salts can still be removed. This was a brand new method to me, but I decided to give it a shot since it seemed like the best bet for the gun tool. 

Electrolytic Reduction in a neutral solution took some time to get the hang of, and I had to use alternative methods to determine salt levels in the solution. However, it was successful and removed the majority of salts from the object! After ER was completed I used a mild chemical bath to remove iron staining from the wood body.

Gun tool after salts have been removed and after chemical cleaning.

Stabilizing the Wood

Now that the salts, staining, and dirt had been removed, it was time to move to the next step of treatment: stability. Waterlogged wood is very fragile and unstable compared to freshly cut or aged wood. This has to do with how damaging excess water can be to wood. If you think about the strength and durability of a wooden table or a tree branch, and compare that to driftwood you found at the beach, you’ll realize that wood becomes very weak when it is waterlogged. 

Wood becomes waterlogged after several years of submersion in water or damp soil. During this time, bacteria will cause cell walls to degrade. Additionally, the cellulose and lignin in wood cell walls will disintegrate, making the wood cell structure very weak. Because of this, wood has to be supported and stabilized before it is dried. Otherwise, it can break or collapse after drying. To stabilize and support the wood, we use polyethylene glycol (PEG) a waxy substance found in a number of household products, like shampoo. In this case, PEG fills the cell walls of wood to support it, so that once the water is removed, PEG is there to provide the support the wood needs. We do this by soaking the wood in a mixture of PEG and water over several weeks. Over time the PEG seeps into the wood and takes the place of water. 

Left: Waterlogged wood cell walls supported with PEG before drying.  Right: Waterlogged wood cell walls have collapsed because they dried without conservation
Source: http://forestpathology.cfans.umn.edu/archaeologicalwood.htm

 

Because the gun sponge is made of several materials, I had a few prepping steps to do before putting it in the PEG bath. First, I needed to remove the consolidating wax I put on the textile. Textiles become waterlogged very similarly to wood, so the textile needed to be treated with PEG as well, and I didn’t want the waxy consolidant preventing that. 

Next, I needed to protect the iron and copper components. While PEG is a great treatment for waterlogged wood, it can be damaging to metals. So when mixing the PEG and water bath, I included a corrosion inhibitor that would both prevent the metal from being damaged by PEG but was also safe for the wood.

In order to let the PEG fully absorb into the wood of the gun tool, it would soak in a PEG and water solution for several months. Each month, I increased the percentage of PEG in the solution, and checked that the corrosion inhibitor was doing its job and keeping the metals preserved.

Up Next

Next week I’ll be back with Part III, where we talk about Freeze Drying wood objects!

 

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