sharp edges going blunt...

[Jodocus]

I have this problem i keep running into:

I first work with a small hammerstone, thin my biface and everything is going nicely. Flakes com off  nice and long. But as the biface get smaller, around 2 inches across:

 

I either stick to the hammerstone and start getting bad step fractures, or I pressure flake and my edges get steeper and steeper until I hit a right angle.

What's going on?

[Outbackbob48]

Jodocus, as your preform gets flatter and smaller it becomes important to start setting up Isolated platforms to make sure your flakes travel and not stallout an stack, as far as your pressure flaking angle getting steeper and steeper is because your flakes are not running past center and are not really thinning pc, It's not getting thicker but as you continue to lose width the edges keep getting steeper. Hope this helps. The flatter my preform becomes the more I have to really pay attention to setting up my platforms an not just striking an hoping not to stack. Bob

[JackCrafty]

To quote Don Tower:

I try to thin the preform as much as possible W/ percussion. I don't like leaving a median ridge in my preforms. If one starts to appear I eliminate it before it has a chance to grow larger. Like everyone else the size of my tools depend on the size of stone I'm working. This was a spall w/ a percussion bulb. The entire percussion thinning was done with a 3/4 copper cap w/ lead in it. When I'm to the point that my percussion flakes need to remove a little more to flatten the blade, but its pretty thin I change the way I use the bopper. Instead of holding the wooden handle I hold it at the cap. Kinda like someone would hold a small hammer stone. Using my thumb, pointer finger,&middle finger. The end of the wooden handle rests in the palm of my hand . Its held in place w/ the ring finger & pinkie.holding it this way gives me great control over the preform. I have to alter my swing , instead of having an arch to my swing I take a sharp, swift. 75 deg angle swing but do it delicately.  At this point your hand holding the preform is as important as the other. Aside from stabilizing the point, my middle & ring finger are used to stop flakes at a determined spot. They can be used to make flakes dive under hinges. Sometimes I use them to push against the flake & this can help to blend two opposing flakes together. Just like pressure thinning. Take the high spots first & work down until its flat. Its kinda hard to explain but I hope it helps. Oh by the way if its not thinning the way I want during percussion I put a little heat to it. No point in working a blade that's not cooperating with me. Tomorrow I will try to finish the point & notch it.

See this thread:  http://www.primitivearcher.com/smf/index.php/topic,28416.0.html

[seminolewind]

Basically at that stage in the game if your platforms are not strong enough your edge will crumble, hinge and stall. Try using pressure to set up your isolated platforms at this stage and once they are set up abrade them well before going back to DP with your bopper. Once the piece is ready to be touched up with pressure same rules apply only on a smaller level. Make sure the small platforms are abraded and set up. Finally push in parallel to the biface with your pressure tool level with the piece. Gradually build pressure till the flake gives way this will drive longer thinning flakes. If your flakes are breaking at a 90 degree angle you are pushing downward not inward like you should.

Just my humble 2 cents worth, good luck and post your results !

[Jodocus]

Thanks guys. It's true I did not really prepare platforms. Also, I shouldd probably use a smaller tool a that statge.
I will try as soon as I get off work.

[Ahnlaashock]

Don't feel too bad.  I can pop flakes that reach or almost reach the other edge in Obsidian with the long flaker, but so far, that ability eludes me with Burlington.  I have the same results you described when I try to use pressure on it.