How To Knap An Arrowhead From A Glass Bottle

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Ingredients (required):
1 Beer Bottle (empty)
1 Hammerstone
1 Pressure Flaker
1 Notching tool
1 Leather Palm Pad (or heavy denim substitute)
1 Pair Goggles
1 Pair Heavy Leather Gloves
1 LARGE box band-aids
1 hammer
1 tarp
1 file (for sharpening the pressure flaker)
1 abrading stone
1 dustpan
1 broom


Step 1: Selecting the Bottle

Don’t overlook the importance of this first step, finding a good bottle to start with will determine how successful your knapping attempt will be. The best part of the bottle to use is the bottom, because the glass tends to be thicker than the sides of the bottle, and much less curved. So when picking your bottle, pay special attention to the bottom.

  1. Colored glass is better than clear glass. Its very difficult to see what you are working on when you work clear glass. Amber or green glass bottles work well
  2. Flat bottoms are crucial. Wine bottles with big kick-ups are not good for knapping. Most bottles have some curvature to the bottom – its best to avoid noticeable concave bottomed bottles in favour of flatter bottoms. (This may entail switching brands of beer – so the decision is not always an easy one)
  3. Avoid bottoms with elaborate embossed markings, like makers marks, numbers, or other designs. These lumps and bumps can be tricky to get rid of.
  4. Begin with a smaller beer bottle before you try a larger flat bottomed wine bottle. They are less difficult to hold and its easier to cover a smaller surface with flakes than a larger one. You can work up to wine bottles.

Step 2: Breaking the Bottle

Now you are going to need to break the beer bottle. You want to break it in such a way that the bottom will not be broken. Throwing it against a wall or rock is NOT a good way to start as the bottom is likely to break. Try wrapping it up in a corner of your tarp or a very heavy plastic bag and hitting the shoulder of the bottle with the hammer. NOTE: Wrapping the bottle up like this contains the mess, it does NOT protect you from the broken glass – The breaking glass can cut through the tarp and plastic bag quite easily. WEAR HEAVY LEATHER GLOVES.

Its easier to break a bottle by hitting it in the middle, but you have a greater chance of breaking the bottom if you hit it there, so strike the shoulder. If you don’t have a hammer, try a hammer stone. Be very careful.

Alternatively, it is possible to cleanly pop the bottom off of a bottle by putting a nail into it (tip down) and shaking it straight up and down with your thumb over the mouth of the bottle. A bigger nail is necessary for wine bottles. I use a round file as a substitute. If successful, the bottom of the bottle will pop out as a sharp glass disc.

Step 3: Cleaning the Hanging Glass off the Bottom

Unwrap your broken bottle. Hopefully the bottom will be in one piece. If it is, it will likely still be attached to sharp glass from the sides of the bottle. You will need to trim these hanging shards off, so that you have a nice flat bottom to work with. Hold the bottom upside down so that the shards hang down. HOLD THE BOTTOM WITH LEATHER GLOVES OR WITH YOUR LEATHER PALM PAD. Brush the hanging glass off with your hammerstone or the hammer. If you have a stubborn shard, try changing the angle you are holding the piece before you try striking harder. Don’t brush too much, you just want the bottom to be flat – too much brushing will make nasty step fractures. Step fractures are failed flakes which break and end with straight edges, rather than gently feathering out. When you are done, look at the bottom and you will see “dents” on the inside of the bottle where you broke the hanging shards off. These dents are flake scars.

Step 4: The Serpentine Edge – Alternate Flaking

Now the fun begins! To knap an arrowhead out of a bottle bottom you need to 1) make a bifacial edge, 2) cover both faces with flakes, 3) shape it, and 4) notch it (optional). Points 2 & 3 will be discussed in the next section, and you don’t have to worry about notching yet. We are going to start by making a bifacial edge all the way around the bottle bottom. A bifacial edgeis an edge which has been worked on both (bi-) sides or faces. Look at your bottle bottom. If you followed the instructions in step 3, you will only have flakes scars from removed hanging shards on the inside of the bottle bottom, and none on the outside. Pieces worked only on one side are called unifacial.

[holding the piece]Ok, lay the bottle bottom flat in the leather pad in the palm of your left hand (if you are right handed), and clamp your fingers down on top, to firmly hold the glass. It doesn’t matter which side is up or down, just make sure that the edge you want to start working is exposed. You should have a little sandwich in your hand which goes; fingers, leather, glass, leather, palm. Now rest the back of that hand against the inside of your left knee for support. Using your copper flaker, you want to push down on the edge and detach a flake from the underside of the glass. [push, don't pry]Don’t pry the flake off, push it off. You really have to push hard to get a flake to come off. If detaching the flake hurts or bruises your palm, double or triple up your leather palm pad.

[alternate flaking, the serpentine edge]The flake removed will look something like a little half cone, and the flake scar will be a negative cone. You can fit the flake back into the scar to see what I mean by a positive cone (flake) and negative cone (flake scar). Ok, put your flake somewhere that people won’t step on it and get back to your bottle bottom.

Flip the glass over so that the flake scar that was on the bottom is now on the top. You will use that flake scar as the platform for your next flake. The platform is the place where you place the tip of the flaker to push a flake off. You want to place the tip of the flaker to the left or right of the center of the flake scar, so that the next flake you remove will be off to one side of this first flake. Again, push down with the flaker and take another flake off. What you should have now is a bottle bottom, with two flake scars: one on each face. Now flip the glass over again and use the flake scar left from the second flake removal to remove a third flake. Continue to alternate flake around the entire edge of the bottle. When you are done you will have a wavy, bifacial serpentine edge!

Step 5: Shaping

Now you have a wickedly sharp, bifacially worked bottle bottom. It doesn’t look anything like an arrowhead yet – why? Its not shaped like one, either in cross-section or outline. The flake scars are only around the edge, they don’t cover the face of the glass yet. You need to pressure flake it into shape. To do this, you need to change strategies a little. Instead of taking short chunky flakes off, like you did to make the serpentine edge, you need to take long, flat flakes off, which cover the faces of the bottle bottom, not just the edges. To do this, you change the angle you are flaking. Instead of pushing down, you want to push into the glass.

Shaping – Cross-section
[lens diagram]If you look at your beer bottle bottom from the side, you will see that it is now, more or less, hexagonal. It has two flat faces and steep bevelled edges. It will also have a slight curvature to it, with a concavity on the bottom face and a slightly convex top surface. Arrowheads are, most often, lens shaped in cross-section. To achieve this lens shape, you need to get rid of all the concave curvature of the glass. In the process you will also be covering the blank faces with attractive flake scars. Most of the work you need to do is on the bottom, concave side of the glass. It will be very tempting to remove flakes from the upper, convex side because flakes love to travel across convex surfaces. The flakes you remove from the bottom will be very short by comparison, but that’s okay. They will get longer as you work at removing the curvature of the glass. Taking beautiful long flakes off of the upper, convex side of the glass will only make the curvature worse.

To remove the cross-section shaping flakes you will need to use the serpentine edge you’ve created. Creating the serpentine edge has made a whole series of platforms. The wavy edge zigzags up and down across the centerline of the edge. This is important. Your edge has peaks which are above the centerline and valleys which are below the centerline. Your edge looks something like this: /\/\/\/\/\/\/\ You use the valleys as platforms to take off flakes. Look at you glass and find the peaks and valleys. The valleys are the platforms. Imagine the centerline. Now flip it over. Find the peaks and valleys. Find the platforms.

[shaping, long flakes]Hold the bottom in your hand, the same as when you made the bifacial serpentine edge. Make sure that the concave face is on the bottom. Find the peaks and valleys. Place the flaker tip against one of the valleys. Instead of pushing down, push into the glass. Push hard, build up a force and then push down a little to detach the flake. Remember push in, then down. Don’t flip the glass over. Instead, move to the next valley and remove your next flake. Go all the way around. Then do it again. Don’t be discouraged if your flakes aren’t very long. You may have to go around the glass 3 or 4 or 5 times before the flakes reach all the way to the center. Everyone’s flakes are short the first time around.

As you knap, your edge will get higher and your platforms (the valleys) will become less pronounced. So you will have to make new ones. You can do this a couple of different ways. One way is to use the tip of your flaker to brush up on the edge. This will remove tiny flakes from the upper surface of the edge (WEAR GOGGLES!). This will get rid of the thin brittle edge, making it stronger and lower. The second way to make new platforms is to grind the edge with an abrading stone. I just use one of my hammerstones. Again, you want to prepare your platforms in the opposite direction that you are flaking. Flip the glass over, so that the face you want to flake is facing up and brush the edge, in a downward motion, with your abrader stone. Flip the glass back over, look for the platforms below the centerline, and keep knapping.

Keep this up until you achieve the desired lens shape. Remember to spend most of your time removing flakes from the concave side. It won’t take you very long to cover the convex side with flake scars.

Shaping – Outline
[shaping, outline]While you are working on the lens shaped cross-section, you will also want to coax your bottle bottom into an arrowhead shape. There are no hard and fast rules for shaping the outline of your arrowhead. If the bottle bottom is circular you can arbitrarily select a pointy end and a base end. Gradually change your circular bottle bottom into a triangle. animated notchingIf your glass is not perfectly round, look for the longest axis, and align your triangle along that. The first step is to stop thinking about the bottle as a circle and start thinking of it as a chubby triangle. Instead of working around and around in a spiral, work from three directions – in from the two sides of your arrowhead and up from the base. When you abrade your platforms, keep the triangle in mind and work towards that goal.

Step 6: Notching

Wow! You made it – you have a lens-shaped triangular arrowhead. All you have left to do is notch it! The notching tools I typically use are sections of coat hanger mounted in broom handles, which have been filed to a chisel shape or copper wire which has been hammered flat (see the Pressure Flaker Page). Pick the point on the edge of the arrowhead where you want to start your notch. Use your notching tool to create a little nick in the edge, the same way you made your first flake on your serpentine edge. Flip it over. Take another flake of in the same place you took the first little flake off. Flip it over and keep doing it. Its the same sort of process as you used to make the serpentine edge, except you are flaking straight into the body of the piece instead of around the edge. Repeat the process for your second notch.

Tip: I like to make both notches at the same time, rather than finishing one and starting on the second one. I find that they turn out more uniform if I work on them together.

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