4.25" x 3"
"8th Century B.C. shipwreck, carriers of wine, Tanit or Elissa", is what's written above the sediment glaze. Interior white and copper green band are glazes assembled from refined materials. Glass from an Egyptian market mixed with clear sea-glass melted in the thumb-well.
This sediment is from amphorae taken at Ashkelon Excavations in the Mediterranean shipwreck sites of either Tanit or Elissa -- both from 8th century B.C. See a photomosaic of the seafloor at the wreck site: Amphorae on Mediterranean Seafloor