Green Ash Hollow Form Vessel with Jet inlay, 8” diameter x 4” tall, walnut oil and Osmo hard wax/oil finish. This piece was made from a branch collar or Callus … When a tree branch is pruned properly, the tree forms an expanded collar of specialized tissue around the cut to heal the wound and compartmentalize decay. This produces interesting grain patterns and bark inclusions similar to burls … though not technically a burl.