http://archaeologyinbulgaria.com/2020/04/18/disc-like-copper-ingots-found-in-ancient-shipwreck-at-bulgarias-black-sea-coast-similar-to-gelidonya-uluburun-shipwrecks-of-mediterranean-turkey/
Disc-Like Copper Ingots Found in Ancient Shipwreck at Bulgaria’s Black Sea Coast Similar to Gelidonya, Uluburun Shipwrecks of Mediterranean Turkey