Raised structure tar (IMAGE) Delft University of Technology Caption Raised structure tar – Birch bark tar vessel containing hot tar from a recently completed experiment using the ‘raised structure’ technique. Credit Photo credit: Geeske Langejans Usage Restrictions No restrictions. License Public Domain Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.