Sand from the sealed Middle Byzantine amphorae of cape Stoba shipwreck

The remains of cape Stoba shipwreck lies on the seabed near Mljet island at the depth between 21 and 28 m. The wreck-site is evidenced by a cargo of amphorae and glass dated back to the 10th-11th century AD. Five amphoras, located in the cargo part of the ship, as well as the small ceramic vessel which had to be placed in the ship’s kitchen, were found filled with sand and closed with a wooden stopper and resin. The aim of this study is a characterization of the sand which could help in the determination of its purpose. Sand samples from amphorae and vessel, as well as from the sea bottom, were investigated. Mineralogical content was determined using X-ray diffraction and grain size distribution by wet sieving. From fine sand magnetic fraction is separated. All granulometric and magnetic fractions were examined by binocular magnifier. All sand samples are marine sediment of carbonate composition. Sand grains are mainly skeletons of the Mollusca, Corals, Foraminifera, Sponges and Echinoderms. This investigation has neglected the archaeological assumption that sand was used as a raw material for glass manufacture. One of the assumptions is that sand could serve as dishwash as it was found in a small ceramic vessel inside the kitchen as well. But, the composition of sand is not suitable for this purpose. It is not possible that sand from the sea bottom entered in amphorae through a small hole at the center of the cap as the coarser grain size were found. Additionally, the depth at which the amphorae were found is below the base of the waves, and the sea currents in this area are not strong enough to produce a significant suspension of seabed material. This sand could serve as a ballast, although archaeologists have not encountered such a case so far.