The caulking material is a unique element of the traditional Scandinavian clinker build ships. It deserves much more attention than what has been the custom in Denmark. The tradition has been to remove the caulking material from the planks before documentation, with little attention or none at all towards the possible information hidden in the caulking.
In 1996-1997 a ship find from Roskilde harbour was excavated by the National Museum of Denmark. The ships are dated by dendro chronology; the oldest to the late Viking age AD 1025 and the youngest to the Middle Ages AD 1420.
Focus is on the caulking material from seven of the excavated ships, one war ship and six cargo ships. The different types of caulking as well as the wool types present in the Roskilde ships is analysed macro- and microscopically. Two systems of categorizing the wool fibres is presented and and the results are discussed. It seems likely that the tradition of the making of the caulking material is different from one area to another. During time the caulking seems to develop from very uneven numbers of yarns spread all over the ship in the Viking age, to a very homogenous and uniform type of caulking in the Middle Ages. Analyses done on the tar from most of the ships will be discussed.