Tuesday, October 13, 2009

Use of Hammer Stone & Soft Hammer Percussion To Create Chips From Large Pieces Of Obsidian (or Flint or Chert)

Some folks have asked about percussion knapping and making small pieces (chips) for making arrowheads from large chunks of knappable stone, such as obsidian.

Once you have a local source of obsidian, then it is useful to have some kind of appropriate hammer device with which to break small pieces off of large pieces. You could use the old type tool, the hammer stone. Get a nice round river rock of granite or some other hard type stone. If it is heavy enough for its size, mass is important for this activity, then you can use it to break corners off of large pieces of obsidian.

Do not try to hit against a flat face on the target stone. Any fracture will initiate going into the mass of the stone, and only create cracks inside the chunk, not break off small pieces which are usable. Instead hit near a corner, and aim the fracture to follow along a ridge or edge on the surface.

Always wear leather gloves, and support the target stone on the ground, or on a thick leather pad. Also wear safety glasses, as small chips will fly.

A modern alternative to the hammer stone is to use a copper billet. I use a copper rod, 3/4" in diameter, by about 5 or 6 inches long. The end is rounded off by impacts. This is heavy enough, yet the metal is soft so it won't crush the target stone.

If you use a steel hammer it will just crush the natural glass.

The idea is to control the fracture. Obsidian naturally fractures in a cone shape, just like glass. If you have ever seen a hole in a thick glass window pane made by a BB, then you will know what I mean by a cone. The fracture radiates out from the point of impact at about 70 degrees away from the line of impact force.

The key is to align this fracture plane just under the face of the piece of stone which you are trying to break. That way the fracture plane travels just inside the stone and travels a good ways as it breaks. This can give you a nice long chip. Remember, you are in control of the stone, so you can tilt it to align the angles the way you want it to break. Practice hitting the stone in the same way or direction most of the time. Then you can modify the breaking angle by tilting the target stone, not changing your swing of the tool.

It takes practice to develop a feel for the angles and the direction of fracture.

I would suggest getting a couple of chunks and just breaking away at it to get the feel for the directions and force needed.

Good luck, and always utilize the safety gear.

F. Scott Crawford
Carrollton, Texas

You are invited to visit my web site for more background information and photographs related to the making of arrowheads: http://www.arrowhead-makeyourown.com/

For fully photo-illustrated process information related to the making of an obsidian Gunther style arrowhead, plus photographs of a number of ancient and authentic Gunther type arrowheads, you are invited to visit my other web site: http://www.arrowhead-maker.com/