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.
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.
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.
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.