Birch bark tar has been used in northern Europe as a superior mastic as far back as 80,000 years. It was found on a Neanderthal spear point, with a thumb print. Pieces of chewed birch bark tar with human teeth marks go back as far as 11,000 years. Otzi’s 5,300 year old copper axe was hafted with birch bark tar. The early Greeks used birch bar tar to glue broken pots together. The Roman Empire was glued together with birch bark tar.
Birch bark tar is a thermal plastic material, that is a solid at 65 degrees Fahrenheit. At 85 degrees Fahrenheit, it is just a bit softer and can be molded in your hands. At 105 degrees Fahrenheit, it is a medium stiff putty. At 135 degrees Fahrenheit, birch bark tar is a softer sticky putty. Birch bark tar boils at about 352 degrees Fahrenheit.
via Birch Bark Tar.