From the hot guts of the earth comes one of the sharpest materials around, obsidian, a stone so sharp it was recently used for precision eye surgery.
When you grow tired of working with glass, obsidian is a great material to graduate to.
With similar properties to modern glass, obsidian has been a knapper’s staple for centuries.
Flint knapping demonstration at the Quarry Hill Nature Center in Rochester, Minnesota.
Unaltered bottle bottom. Be sure not to slice off or into your digits.
Trimming the edge. Again, you might want to opt for gloves.
The completed trimmed edge.
Here is the prepared platform.
The author abrading the piece’s edge with an easy-to-handle stone.
Time to get a grip on pressure flaking.
The platform with thinning flakes.
A look at the thinned bottle bottom.
Decide where to “draw the triangle.”
The “rough” arrowhead is really starting to look like something.
The finished piece—not too shabby!
When you can make stone tools, the whole world is your pocketknife. The ground is littered with rocks brimming with the potential to become hammers, axes, arrowheads, knives, awls, sanders and more. From humble beginnings, flint knapping has evolved from smashing rocks together to a deep engineering art form. Crude stone tools can be very effective, but with practice you can make functional works of art from the bones of the earth.
Learning how to turn glass bottle bottoms into arrowheads is a great way to start knapping. Glass is readily available and has the right fracture pattern for flint knapping. Fine-grained crystalline stones, like glass, obsidian and flint, will produce flat, conical flakes if struck correctly. It is this quality that allows flint knappers to turn rocks into arrowheads, knives and more. For this project you will need a large tarp; an outdoor work area; safety glasses; closed-toe shoes; long pants; a palm-sized leather or flat rubber pad; a larger piece of canvas or leather for a leg pad; a small abrasive stone; a 4-inch nail; a 3-inch length of thick copper wire or a copper nail; and a 6-inch piece of broom handle to make a pressure flaker.
The first step is to consider a few safety precautions. Flint knapping is not exactly dangerous, but you do run the risk of cuts, punctures, eye injury and silicosis. Make sure to wear safety glasses. Not all flint knappers wear gloves, but if you want extra protection, wear a thin glove on your non-dominant hand or tape your fingers. Long pants and shoes are also a good idea. The biggest safety issue to consider is silicosis. Silicosis is a disease that can be acquired from years of knapping inside. You can easily avoid it by knapping outside. Some knappers will use a fan to create a slight cross breeze over their workspace. Finally, lay out a large tarp to catch any broken glass and keep your yard barefoot friendly. Also, keep a box of bandages nearby.
Giving It Shape
Before you break any glass, lay out a ground cloth, gather your tools and make your pressure flaker. To make the pressure flaker, find a stick, a section of broom handle or a large dowel rod to use as a handle. It should be about 6 inches long. Hammer your copper nail into the tip of the handle, leaving roughly two-thirds of an inch sticking out. With a hacksaw, saw off the end and then use a coarse file to sharpen the pressure flaker into a point. You can also drill a hole in the handle and glue in a piece of thick copper wire if you can’t find copper nails. Now put on your safety glasses, because it’s time to start knapping!
You need to remove the bottom of the bottle first. If I don’t have a 4-inch nail lying around, I usually fold the tarp edge over the bottle and strike the neck with a stone until it breaks. This method is effective but does produce unnecessary shrapnel. For a clean, safe break, stick a 4-inch nail into your bottle with the point down. With your thumb over the mouth, shake the bottle until the bottom pops off.
Take a look at your raw material. Your goal is to thin the glass down into an arrowhead with an even, flat surface on both sides, and an edge that runs along the center mass of the arrowhead. Can you visualize an arrowhead in the glass? Where is the excess material that needs to be removed? What is the angle of the edge of your glass? You will need to remove any of the bottle sides that remain attached to the bottom first. You can get rid of excess material quickly by trimming with the pressure flaker. To trim, hold the edge of the excess glass against your lap pad and use the tip of the pressure flaker to apply force down towards your leg on the edge of the glass. Use this technique to get rid of the bottle sides.
In order to remove thinning flakes from any project, you need to create an angle on your piece’s edge. This is called a platform. You will need to create a striking platform with an angle that is between 20 and 60 degrees. To do this, hold the glass against your lap pad with the concave side down. Hold the edge of your glass at a slight upward angle and use the tip of your pressure flaker to push down on the knife edge of the glass. Apply pressure towards your lap pad to remove a flake. Trim the edge of the glass all the way around with this technique. Flip over your glass. There should be a good edge angle of 20 to 60 degrees.
Now, you must strengthen and prepare the edge or platform by abrading excess material off the edge with your rough stone. Abrasion gets rid of weak, brittle material on the platform edge, allowing the force of your pressure flaker to travel deep into the stone. Use your abrasive stone to grind down and across the edge. Almost anytime you remove material you will need to prepare your platform edge with abrasion.
The platform edge is ready for thinning and shaping. This will require a slightly different technique than trimming. Grab your palm pad and place it in your hand, then put the bottle bottom on the palm pad and support the back of it with your fingers. Use the tip of the pressure flaker to apply inward pressure directly to the fine “knife” edge of the glass. Drive pressure through the stone to the other side and then apply outward pressure toward your palm to remove the flake. Built-up inward pressure helps drive a flake across the face of the glass and the outward pressure pulls the flake off.
When you are removing flakes, the flake will follow the angle of the pressure flaker. Pull thinning flakes off the glass all the way around until you come back to where you started. Abrade and then make one more thinning pass around your piece.
Making A Point
Draw a triangle that is roughly the shape of the arrowhead you want on the glass with a marker. Hold the glass against your lap pad with the side you just thinned down. Use the pressure flaker to trim the glass into the shape of the triangle you drew. Now you have a piece of glass that is roughly arrowhead shaped with a roughly 90-degree angle on the edge. Before you can thin the convex face of the arrowhead, you must change the angle of the edge again.
Hold the glass with the concave side against your palm pad and take some short flakes all the way down the edge. This should change your edge angle to something close to 60 degrees. Abrade down and across the edge, and place the convex side of the arrowhead against your palm pad. Use your pressure flaker to remove thinning flakes along the edge. Change the edge angle of the other side of your arrowhead in the same way and thin that edge as well.
Your arrowhead is getting close to being thinned. Pause again and look for concavity and convexity in your piece. You will notice that the tip and back of your arrowhead have retained the concave edge shape of your bottle bottom. Abrade and remove a few thinning flakes from each end to correct this. Once this is accomplished, you are ready to complete the shape and edge of your arrowhead.
Examine your arrowhead. What material needs to be removed? Make a few more passes on both faces of the arrowhead to help thin the material. Focus on the shaping, thinning and creating a sharp point.
When you are finished shaping your arrowhead, you can finish it with a notch. For a basic side notch, use your pressure flaker to cut in a notch on either side of the arrowhead. Or, if you want to keep it really simple, use the pressure flaker to remove material from the center of the bottom of your arrowhead, leaving two tails on either side of the back. With notches, your arrowhead is complete.
At first, you will probably ruin as many arrowheads as you make, but with practice, you can make effective glass and stone points. Arrowheads do not have to be pretty to do their job, but over time you will find yourself turning out works of art.
In the end, if all this technical information is overwhelming, just grab your pressure flaker and glasses, experiment wildly, eyeball it and have a good time. Flint knapping is truly an art form, and from this small seed of knowledge you can begin a journey of surprising breadth and depth that will last for years. Stick with it, be patient and take your time. Nothing will snap your arrowhead like haste.
This article was originally published in AMERICAN FRONTIERSMAN. Subscription is available in print and digital editions here.
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