I had some wooden spools that I found in my Aunt's house. I obtained a 2 qt. canning jar that was my Grandmother's and made a lamp. dH modified a lamp kit purchased at the hardware store, and a lampshade. Ta da- vintage lamp. Some of the spools still had thread on them and others were empty. I put torn strips of fabric around the empty ones. The shade was covered with verticle strips of torn fabric also. It's very cute for a sewing area and I saw one in an antique store.
As for washing the, the empty spools would be easy. If there is not much thread on them, I would treat them as empty. But I think if there is a lot of thread on them, they might get musty-smelling if dried slow. I wonder if you could dry them outside in the sunshine?