For as long as humans have sailed, ships have needed protection from water, salt, microorganisms, and those pesky marine worms that think your hull is a snack. Yet until the mid-20th century, researchers gave the non-wood bits of ancient ships about as much attention as a captain gives to a leaky bilge pump. Waterproofing materials, in particular, remained understudied - until now.
A new study in Frontiers in Materials is helping fill that gap. Researchers in France and Croatia analyzed the protective coating on the Roman Republic shipwreck Ilovik-Paržine 1, which sank about 2,200 years ago off the coast of what is now Croatia. Because nothing says 'Roman engineering' like a boat that lasted long enough to sink and become a museum piece.
"In archaeology, little attention is paid to organic waterproofing materials. Yet they are essential for navigation at sea or on rivers and are true witnesses of past naval technologies," said first author Dr. Armelle Charrié, an archaeometrist at the Laboratory of Mass Spectrometry of Interactions and Systems in Strasbourg. "Studying the coatings, we found two different kinds on this vessel: one made of pine tar, also called pitch, and the other of a mixture of pine tar and beeswax. Analysis of pollen in the coating made it possible to identify the plant taxa present in the immediate environment during the construction or repairs of the ship."
The wreck was discovered in 2016, and both vessel and cargo have been investigated several times since. This study is the first to combine molecular and pollen analysis to identify the ship's coatings and reconstruct the vegetation present when those materials were produced and applied to the hull. The research was a collaboration between the Department for Underwater Archaeology of the Croatian Conservation Institute and the 'ADRIBOATS' program of the Centre Camille Jullian at Aix-Marseille University in France.
"Some regions throughout the Adriatic have particular characteristics that led local populations to develop a specific shipbuilding style," said Charrié. "Only studies like ours offer an overview of these traditions which bear witness to genuine know-how and diverse traditions." Because, of course, even ancient shipwrights had regional preferences - like choosing between pine tar or pine tar with a hint of beeswax.
To investigate, the researchers performed structural, molecular, and pollen analyses, using mass spectrometry to identify unknown substances within complex organic mixtures. They analyzed 10 coating samples to determine the biological origins of the natural materials. Molecular fingerprinting revealed compounds associated with pine trees, showing every sample was dominated by heated coniferous resin or tar - also known as pitch. One sample, however, contained a different formulation made from beeswax and tar, a mixture known to Greek shipbuilders as zopissa. This blend improves the adhesive's flexibility and is easier to apply when hot - because who wants to wrestle with sticky tar at room temperature?
Pitch is naturally sticky, so it can capture pollen from nearby vegetation and preserve it for millennia. By studying the types of pollen trapped in the coatings and measuring their relative abundance, the researchers narrowed down where some of the pitch may have been produced or reapplied during repairs. The pollen from Ilovik-Paržine 1 pointed to a wide range of environments: Mediterranean and Adriatic coasts and valleys with holly oak and pine forests, plus matorral - a Mediterranean shrubland where olive and hazel trees grow. Alder and ash pollen indicated riverbanks and seashores, while small amounts of fir and beech suggested mountainous terrain characteristic of the north-eastern Adriatic coast, where the mountain ranges of Istria and Dalmatia sit close to the sea.
The analysis also suggests the vessel received four to five separate batches of coating over time. The stern and central section appeared covered with the same material, while researchers identified three distinct coating batches at the bow. That pattern may indicate repeated repairs, with materials sourced from different locations around the Mediterranean. Earlier research on the vessel's ballast pointed to Brundisium (today Brindisi) on Italy's south-eastern coast as the ship's birthplace. The new pollen evidence suggests some coatings may also have been applied there, while other layers were added along the north-eastern Adriatic coast, close to where the wreck was found.
"While it seems obvious that ships sailing long distances need repairs, it's simply not easy to demonstrate this," concluded Charrié. "Pollen has been very useful in identifying different coatings where the molecular profiles were identical." So next time you're slapping tar on your boat, remember: you're part of a 2,200-year-old tradition, and the pollen will tell future archaeologists exactly where you've been.