Since we have a few new knappers, I thought I'd diagram a small turtleback I took care of on the big point I finished last night. All of you know I'm not an expert, but since I was a newbie not that long ago I thought I might be able to take some pictures that'll help the new knappers understand how platforms are the key to thinning. Goodness knows I'm still learning this, but it worked out nicely this time and thought it might be helpful. I didn't take a picture of the original spall but it was a little smaller than my hand and it had a nasty divot where some water in the stone had blown out when it was heat treated. I didn't expect to get a point, but when I'd gotten to a preform with the bopper I decided to capture the process in pictures.
There was some concrete on one side and when I hit it the stone began to step fracture on both top and bottom of that side. I abandoned the bopper at that point and went to indirect percussion (since I'm a Patrick student).
I ran a complete pass on all 4 edges getting good thinning at first, but then leaving a nice hump on one side. The concrete stopped the flakes and I botched some hits on the other edge to get me in trouble. So, I ran a shallow set of flakes on the opposite side from the hump trying to raise the edge high enough to take long flakes on the other side in an attempt to knock it off. Since I'm holding the stone with the hump down, the platforms will appear as low spots in the pictures. The important thing to remember is that the edge needs to be closer to the side you want to remove thickness from than the other side. When I was done I had 2 ridges I could exploit with corresponding platforms. One is dead center and the other is to the right. The point is turned away slightly so you can see the ridges.
This picture shows the edge and I edited it to better point out the platforms. You can see how the edge is moved towards the face I want to drive the long flakes on.
One tip here. For a long time I thought the secret to long flakes was driving into the stone more but that's not necessarily true. What I've been learning is the secret to long flakes is a good platform and then a great amount of force (in my case that means a powerful swing with the mallet into the punch). I've gotten a lot less step fractures as I've worked more on platforms and less on increased angles. Not sure that made sense but it's what I've been learning lately. After whacking those 2 platforms the face looks like this and I'll highlight the flakes that were removed.
That left the edge like this (you can see how much thickness was removed). Too bad I didn't get the picture taken directly from the side.
You can see that a new ridge was created between the flakes and I went ahead and exploited that as well but didn't get that good a flake.
At this point I went on taking passes down each edge. I still ended up with a thicker spot towards the base which I thought I could knock off with a flute.
But, it didn't quite work out that way, consequently the point ended up heavier than I wanted. I punch notched it, since it was so thick. This picture shows the punch, made from a hard copper wire hammered flat and notched with a file. The final point weighs in at 343 grains...a little to heavy for my cane arrow shafts. Still, I like it and will haft it up as a short knife.
I hope the pictures will help the new guys as they work to figure out this wonderful addiction.
George
