In lithic analysis, a subdivision of archaeology, a bulb of applied force (also known as a bulb of percussion or simply bulb of force) is a defining characteristic of a lithic flake. Bulb of applied force was first correctly described by Sir John Evans, the cofounder of prehistoric archeology. However, bulb of percussion was coined scientifically by W.J. Sollas. When a flake is detached from its parent core, a portion of the Hertzian cone of force caused by the detachment blow is detached with it, leaving a distinctive bulb on the flake and a corresponding flake scar on the core. In the case of a unidirectional core, the bulb of applied force is produced by an initiated crack formed at the point of contact, which begins producing the Hertzian cone. The outward pressure increases causing the crack to curve away from the core and the bulb formation. The bulb of applied force forms below the striking platform as a slight bulge. If the flake is completely crushed the bulb will not be visible. Bulbs of applied force may be distinctive, moderate, or diffuse, depending upon the force of the blow used to detach the flake, and upon the type of material used as a fabricator. The bulb of applied force can indicate the mass or density of the tool used in the application of the force. The bulb may also be an indication of the angle of the force. This information is helpful to archaeologists in understanding and recreating the process of flintknapping. Generally, the harder the material used as a fabricator, the more distinctive the bulb of applied force. Soft hammer percussion has a low diffuse bulb while hard hammer percussion usually leaves a more distinct and noticeable bulb of applied force. Pressure flake also allowed for diffuse bulbs. The bulb of percussion of a flake or blade is convex and the core has a corresponding concave bulb. The concave bulb on the core is known as the negative bulb of percussion. Bulbs of applied force are not usually present if the flake has been struck off naturally.
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vignette|upright 1.2|Biface acheuléen en silex de Saint-Acheul Un biface est un outil de pierre taillée caractéristique des périodes anciennes de la Préhistoire. Il fait son apparition au Paléolithique inférieur en Afrique de l'Est et se diffuse en Europe et en Asie durant cette période. Il est particulièrement caractéristique de l'Acheuléen mais est encore présent au Paléolithique moyen, en particulier au cours du Moustérien récent. Le mot « biface » a été proposé en 1920 par A.
vignette|redresse=1.2|Démonstration de débitage par pression avec une béquille abdominale longue ; tailleur J. Pelegrin, CNRS (14 janvier 2011, Université du Mirail, Toulouse) La pression est une technique de taille des roches dures utilisée depuis la Préhistoire. Elle consiste à détacher des éclats de matière non pas par percussion mais en exerçant une forte pression sur la roche taillée. Elle est utilisée pour le débitage et pour la retouche. Le débitage par pression est la technique qui apparaît le plus tardivement au cours de la Préhistoire.
In lithic analysis, a subdivision of archaeology, a bulb of applied force (also known as a bulb of percussion or simply bulb of force) is a defining characteristic of a lithic flake. Bulb of applied force was first correctly described by Sir John Evans, the cofounder of prehistoric archeology. However, bulb of percussion was coined scientifically by W.J. Sollas. When a flake is detached from its parent core, a portion of the Hertzian cone of force caused by the detachment blow is detached with it, leaving a distinctive bulb on the flake and a corresponding flake scar on the core.