In addition to winding thread around the arrow shaft to secure the feather fletchings, glue was sometimes also used, with verdigris occasionally added to help stop infestation of the feathers by mites.  The lump of birch bark tar in the picture was discovered in an early Medieval cemetery at Hatherdene Close, Cherry Hinton, Cambridge, and would have been used as a glue for hafting weapons and fletching arrows, as well as more peaceful activities such as waterproofing and repairing pottery vessels.

 Image reproduced with the kind permission of the University of Bristol.