|Angle of Blow (AOB) -- I measure the AOB from the "driving-nails-vector", which is a line through the platform and the support of the core. This AOB is different from the one used by most authors (Pelcin 1996:83, Whittaker 1994:94), which is measure from the platform face. The significance of this difference is when I write, "increasing the AOB" it would be "decreasing the AOB" in the nomenclature of the other authors.
The driving-nails-vector is defined as the direction of the force that will not rotate the core. It will only compress the core. On large cores where the inertia of the mass becomes the support for the core, then the driving-nails-vector would pass through the platform and the center-of-mass.
I measure from the driving-nails-vector instead of the platform face because it makes the AOB independent of the platform angle. By separating the two, I can investigate the effects of one while holding the other constant. I have found that AOB is the dominant variable of the two with regard to their effects on flake morphology. However, since AOB is not preserved in the archaeological record, then platform angle is a good proxy for it since most off-margin strikes are perpendicular to the platform face.
|Cycle -- The motion that repeats itself in a vibrating system. A cycle is the vibration during the period. |
|Flake Types -- I recognize the four common flake types of feather, hinge, overshot (or reverse hinge), and step that are found in most of the literature (Cotterell and Kamminga 1987:684; Patten 1999:85; Whittaker 1994:18). Plus, I add the full-length flake for a total of five. These types are defined by their crack trajectory and termination and not by their initiation. Each, with the exception of the hinge flake, can be created with either pressure or percussion (soft or hard hammer). Each can have the universe of bulbs of force. And, each can initiate under the force application tool or away from it (lipped flake). The factors that effect the creation of the various flakes are width-to-thickness ratio of the core, loading time of the force, and angle of blow.|
|Feather Flake -- a flake created by a single crack with a straight trajectory that exits the front face of the core. Therefore, it is a fractional flake or is shorter than a full-length flake. When these flakes are removed from a flat face, they are wedge-shaped as in the image. The flake scars of these flakes can have some heavy ripples at the end, but the trajectory of the crack is still straight.|
|Full-Length Flake -- a flake created by a single crack with a straight trajectory that runs the full length of the core. As the crack approaches the far end of the core it will often turn, either toward front or back face, but it still exits the bottom of the core.|
|Hinge Flake -- a flake created by a single crack with a straight trajectory until it suddenly, but gently turns towards the front face and terminates the flake. It is a fractional flake or is shorter than a full-length flake. Often as the crack approaches the front face, but long after it has turned toward the front face, it will again turn either up of down. If it turns up it creates the classic lip (reflexed termination) that is associated with hinge flakes. If it turns down, then the flake scar (inflexed termination) is often assumed to be that of a feather flake with a jump in the scar surface. The hinge flake is the only flake that can not be created with pressure.|
|Overshot Flake -- or reverse hinge flake is created by a single crack with a straight trajectory until it suddenly, but gently turns towards the back face and terminates the flake. It has a trajectory that is the reverse of the hinge flake and hence, the second name "reverse hinge flake". It is a fractional flake or is shorter than a full-length flake.|
|Step Flake -- a flake created by two cracks. The first crack is a straight trajectory that actually stops in the core because it consumes all the energy. When the first crack stops, a second crack caused by the knapper's follow-through breaks the flake off. It is a fractional flake or is shorter than a full-length flake. As in the drawing, evidence of the first crack extending beyond the end of the flake scar is almost always present because the second crack rarely begins at the very end of the first crack.|
|Length-to-Thickness Ratio -- Maximum length divided by maximum thickness.|
|Loading Time -- The force application time it takes to raise the force on the platform to the platform strength. I assume the force increases linearly with time until the crack initiates, which is symbolized by the red star. After the crack initiates, the force on the core (not the flake) drops to zero.|
|Margin/Off-Margin Platform Locations -- Off-margin (off-edge) platforms are located away from the edge. Margin platforms are located on the edge. The arrows mark the platforms on the almost identical two cores. The difference between the two is the margin has been moved (reduced) in the core on the right. Margin platforms are usually associated with soft hammer percussion and pressure flaking.|
|Period -- The time (usually measured in seconds) to complete one cycle of a vibrating system. The period is the reciprocal of the system's frequency.|
|Platform Angle -- is the angle formed by the intersection of the platform face and the dorsal face of the core. See image "A". It is an easy variable to measure on a core and most research studies obtain this datum.
Platform angles are not as easy to measure on flakes. The flake in image "B" has an exaggerated reduced margin on the right edge of the image. Does one measure the angle between the platform face and the bevel that created the reduced margin or should one measured it from the true dorsal face? Image "C" is a flake created by a margin strike and the crack initiated at the point of impact, which removed all the platform face. Where does one measure the platform angle on this flake?
Most platform angles in the archaeological record range between 50 and 60 degrees regardless of time or space. For example, this range can be seen on Levallois cores (Van Peer 1992:24) or Folsom, channel flake preforms. When a platform is constructed (edge is turned) to remove flakes from a particular face of the core, it is done in a manner that minimizes the loss of the width or length dimension. The natural outcome of this minimizing effort is a platform angle between 50 and 60 degrees. Further support for this concept is the resharpening bevel on knives and points. These were hafted tools and the owner wanted to maximize their use life. So, they were beveled in a manner that minimizes the lost of material. The bevel on these tools is always between 50 and 60 degrees.
Many researchers have noticed relationships between platform angle and flake geometry. These same researchers also measure angle of blow (AOB) from the platform face, which couples the two variables (platform angle and AOB) and makes them dependent on each other. If angle of blow is measured independently of the platform face, the variation in flake geometry is a result of the angle of blow and not the platform angle. However, since AOB is not preserved in the archaeological record, then platform angle is a good proxy for it since most off-margin strikes are perpendicular to the platform face.
|Platform Strength -- The force that must be applied to initiate a crack.|
|Quarry Artifact -- A bifacial artifact with step and/or hinge flake scars and a width-to-thickness ratio less than 4.5.
The biface fragment in the image is from an Archaic quarry in West Texas. The width-to-thickness ratio is 3.4 and the white arrows mark the termination of hinge flakes. It was purposely fragmented with a burin blow.
|Reduced Margin -- See Margin/Off-Margin Platform Locations.|
|Width-to-Thickness Ratio -- Maximum width divided by maximum thickness.|