Circular Reasoning

Another one of those cases where I get so excited in creating a Foundling that I haven't completely worked out the piece. Here, and old carpenter's plane, a fireplace grill and a lid from a Shaker's box went together so smoothly that I didn't have the time to find that final piece to finish it off. So I am left with an exposed nut that I need to cover. I do have something that may fit but it might be bone or it might be plastic. If it's bone, it fits my aesthetic. If it's plastic, I don't want to use it. So I'm looking for that perfect little item. Nice to be working in the round.