At the successful completion of Stage 6, the preform had been fluted on Face A (bottom in the image) and Face B (top) was usually a flat or irregular surface. Stage 7 had the purpose of creating a ridge on Face B for the second channel flake to follow when it was removed. This was accomplished with controlled pressure flaking which removed small flakes from Face B. These flakes originated at the lateral edges and terminated in the center of the face. During the process, Face B became convex and the preform became thinner and narrower1.
The cross-section labeled "Stage 7" in the image attempts to depict the preform at the end of that Stage. The solid line on Face B represents the top of the ridges between the pressure flake scars. The dotted line represents the bottom of the pressure flakes scars. The difference between the two lines was the thickness of the pressure flakes. Near the preform's lateral edges the pressure flakes were thick because of the "bulb of force". As they approach the center of the Face they thinned out. The cross-section defined by the dotted line depicts a ridge on Face B and this was the ridge the channel flake was designed to follow when it was removed2.
Stage 7 and Stage 4 were identical processes except they were applied to different faces. Stage 7 artifacts represent about 5% of the failures in the archaeological record and I have no Stage 4 artifacts. This lack of artifacts from these two Stages suggests that they were easily accomplished and/or had a low risk of failure.
Stage 7 artifacts are characterized as preforms with a single flute on Face A and some evidence of pressure flake shaping on Face B. Stage 7 artifacts retain the remnants of the platform that was created and used to remove the channel flake from Face A . In different words, the bevel created in Stage 5 on the proximal edge of the preform is still present on Stage 7 artifacts.
This artifact, a proximal fragment of a preform, is a classic Stage 7 failure. The channel flake has been removed from Face A (left image) and the pressure flake shaping is visible on Face B (right image). Failure occurred while performing the pressure flaking. The presence of this pressure flake shaping permits one to assume that the Face A channel flake was successfully removed to the satisfaction of the Folsom knapper. The bevel in the basal concavity (difficult to see in this image) was prepared for the removal of the Face A channel flake. This is proof that this was not a failure during Stage 8--Channel platform preparation (Face B).
This is another proximal fragment. Face A (left image) was successfully fluted because the pressure flake shaping of Face B (right image) had been initiated. It had not progressed as far as in the first image before failure. Note, the remnants of the original percussion work (Stage 3) in the lower right corner (right image). One can see the beginnings of the pressure flake shaping in the scar coming in from the middle of the right edge (right image). This meets one from the left side in the center that was almost lost with the failure. Finally, the proximal edge (right image) is still beveled from removing the Face A channel flake.
This is a split, midsection fragment. The image is not the best, but I have included it to allow me to discuss if this artifact belongs to Stage 7 or not. Face A (left image) had been successfully fluted (Stage 6). I know this because there is pressure flake shaping on Face B (right image). Additionally, the pressure flake shaping appears to be complete over the entire artifact. So did this artifact failure during Stage 7 (pressure flake shaping) or during a subsequent stage? Since the proximal edge is not present I cannot determine if the platform for channel flake B's removal was prepared (Stage 8). It is also possible Stage 8 was completed and this failure represents Stage 9. So did this failure occur during Stage 7, 8 or 9?
I suggest the failure occurred during the channel flake removal from Face B (Stage 9). I further suggest it was caused by the Face B channel flake plunging into the preform. There are three reasons for this opinion. The first is that Stage 9 failures are the most numerous in the archaeological record and, therefore, probability favors this choice. The second is that split preforms were a common failure mode during channel flake removal. The last and strongest reason is the break on the proximal edge (bottom) which is curved in a manner that is identical to the shape of breaks associated with channel flakes plunging into the preform3. (I apologize for the difficulty in viewing the break on this artifact. The next image has a better view of the same kind of break.)
A distal fragment of a preform that failed during Stage 9, "Channel flake removal (Face B)". This artifact is shown here to further depict the pressure work on Face B (right image) prior to channel flake removal. The channel flake scar in the left image is on Face A. An interesting feature of this artifact is the break on the proximal edge (bottom) of the left image. This is where the Face B channel flake plunged into the preform and broke off (snapped off) the distal end.
1 The extreme distal end (tip) of the preform was usually not pressured shape, but left unworked. This left a thicker mass at the tip of the preform. Additionally, the distal edge was usually ground (rubbed on a stone) and often purposely or naturally beveled. These characteristics have led archaeologists to suggest the distal end of the preform was held against an anvil when the channel flakes were removed.
2 Verbal communications from Dr. Bruce Bradley between 5 and 10 years ago.
3 The distal fragment of the obsidian preform in the 3rd image on the Stage 6 page is the identical failure.