I could have coated each with a clear coat lacquer to maintain the shine. However, I am choosing to leave the seal off and let them patina - over time they will turn a nice green color.
I purchased these caps from The Metal Peddler - a family owned company that makes custom copper items. These fence post caps were reasonably priced. They look nice and will protect the post caps from water build up and help preserve the life of the posts. They also fit in with the handcrafted Japanese look I am trying to maintain (especially after they patina).