A straight ridge is necessary to guide the removal of the first blade from a core. If a natural ridge is not present, one can be produced by flaking on the core face. Such a ridge is created by extensive flaking perpendicular to the length axis of the core. The removal of this primary ridge blade, or crested blade, leaves straight scars on the core face which serve as guides for further blades (see Owen 1982, 3). Crested blades have also been described as follows: First blade removed from a core. Bears bi-directional flake scars on the dorsal surface, the result of the worker preparing a ridge to guide the blade (Crabtree 1982,, 41).
see movie on how crested blades are made