Bulb of percussion is a key diagnostic feature in lithic technology and archaeology, referring to the swelling or convexity that appears on a flake just below the point of impact where it was struck from a core. It is one of the most important attributes used to identify human-made stone tools.
🌍 Definition
- Bulb of Percussion: A raised, rounded area on the ventral surface of a flake, formed by the force of a blow during knapping.
- Formation:
- Created when a hammerstone or other percussor strikes the core.
- The shock wave radiates through the stone, detaching a flake and leaving a bulb at the point of force transmission.
🔑 Archaeological Contexts
- Lithic Analysis:
- Presence of a bulb of percussion distinguishes human-made flakes from naturally broken rocks.
- Helps archaeologists identify knapping techniques (hard hammer vs. soft hammer percussion).
- Associated Features:
- Striking Platform: The surface where the blow was delivered.
- Ripple Marks: Concentric waves radiating from the bulb.
- Eraillure Scar: Small secondary flake scars near the bulb.
- Technological Insight:
- Different percussors (stone, antler, wood) produce different bulb characteristics.
- Softer hammers often yield diffuse bulbs, while hard hammers create pronounced bulbs.
📚 Importance in Anthropology
- Human Behavior: Evidence of intentional tool production.
- Cultural Identity: Different lithic traditions can be distinguished by flake morphology.
- Comparative Value: Bulbs of percussion are absent in most natural fractures, making them diagnostic of human agency.
- Material Culture Link: Connects geology (fracture mechanics of stone) with human technological skill.
In short: The bulb of percussion is the diagnostic swelling on a flake’s ventral surface, proving intentional human knapping and serving as a cornerstone of lithic analysis.
