Enfield Rifle Treatment – Using SP-11 2017-04-25T02:59:21+00:00

Enfield Rifle Treatment with SP-11

By Nathan Henry, NC Office of State Archaeology

I have used the SP-11 on an Enfield stock (several fragments including a butt), a fragment of a pine log-boat, a wooden electrical conduit, and several wooden grave markers.

The Enfield fore-stock fragments did really well and exhibited equally good dimensional stability compared with Carbowax (PEG). The butt-stock did exhibit some shrinkage, indicated by some internal checking but the exterior remained dimensionally stable. I may not have left it in the solution long enough. The SP-11 does seem to bleach the gunstock fragments slightly (walnut?) but not so much the pine.

caption

Photo of Enfield rifle butt straight out of solution – still has excess on surface. April 2011.

capp

Artifact after dehydration complete. Light color, some shrinkage but not visible from side. Hardware fits perfectly (wouldn’t fit if shrinkage is significant). June 2014.

What I have found is that the more degraded the wood is the better SP-11works. The grave markers were badly degraded by insect and microbial decomposition and look the same post-treatment as when they were recovered (a good thing), except for some discoloration of the lichens that were still attached. The badly degraded log-boat fragment was immersed and probably fared the best, with no dimensional change or cracking. Using wood-conservator’s language: SP-11 is suitable as a bulking agent and superior as a consolidating agent. It actually adds some strength to the wood without adding weight.

ca

SP-11 treated artifact on top after 2 coats of linseed oil (to darken slightly). PEG 1500 artifact on bottom – although not as nice of a specimen, you can easily see the difference in the color (very dark brown). This has been typical of the experiments. Those treated with polyethylene glycol to be darker and heavier and much more hygroscopic than those treated with SP-11.

To sum it up, for lightly degraded wood where bulking is required, a low molecular weight PEG is possibly superior. I think it may penetrate the wood cells somewhat better. For more degraded wood, where a higher molecular weight PEG is normally used (consolidation), SP-11 is superior, particularly if the final weight of the artifact is a consideration.

Comment from Preservation Solutions:

SP-11 is a small molecular weight polymer and we have found that when soaked long enough the SP-11 will penetrate lightly degraded wood thoroughly.
I’m very interested in exploring the product’s use in log-boat (dugout canoe) conservation. Because it does not add much weight to the finished product (unlike PEG and sucrose that add significant weight) the artifact would be much easier to transport and display. One of the problems with large wooden artifacts like canoes is that their own weight can cause breakage if not constantly well supported. I think this is where the product will really shine due to the lighter weight of the finished product. Plus log boats are often too large to display in controlled environments.

I’m still looking for a sponsor to provide the capital for enough SP-11 to preserve a log boat. I definitely would want to use immersion rather than external application. When I do, I know of several boats now in wet storage and the local waterways that would be good candidates. The good thing is once I get the critical amount, numerous boats could be done with the same solution.


Nathan Henry is an Assistant State Archaeologist and Conservator at the Underwater Archaeology Branch of the NC Office of State Archaeology.