You should always use eye protection when flint–knapping as the shrapnel from the flint flies unpredictably and can easily blind you (or anyone near you). Equally dangerous are the chippings you make, they are razor sharp, so be careful not to get them in clothing or to stand in bare feet in an area where you have been working. You will inevitably get some minor cuts to the hands and fingers when you practice this technique, so be prepared for that.
Flint–knapping (also known as "Flaking" or "Chipping") is one of the ancient methods used to make weapons and tools from stone. It requires knowledge of the process, takes practice and can be somewhat "hit and miss" because fault lines in the stone can cause it to break unpredictably.
Bear in mind that you risk injury when flint–knapping and always turn away as you strike flint to protect the eyes if you have no eye protection. Even minor cuts can turn septic in the wilderness, so weigh up the risks versus the needs before embarking on making stone tools. Tiredness and fatigue can cause a loss of concentration and this could cost you your eyesight; take your time and think about everything you do before doing it.
NEVER heat up stone and drop water on it to crack it, doing this may result in razor sharp shards flying unpredictably and can result in serious or fatal injury. This apart, you are unlikely to end up with a workable piece of stone, so control the process and work only by hand.
Understanding a little about how the chosen stone reacts to hard and softer pressure gives a better chance of success. Arrowheads, spearheads, stone knives, axes and hammers are examples of the sort of weapons and tools that can be successfully made from stone. Of course, you need to be in an area where you can find "glass–like" stones, such as flint chert, obsidian, etc. The best results are from flint.
Flint occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones (see photo above showing a line of dark flint in a limestone escarpment). Inside the nodule, flint is usually dark grey, black, green, white or brown in colour and often has a glassy or waxy appearance. A thin layer on the outside of the nodules, called the cortex, is usually different in colour and is typically white and rough in texture. From a petrological point of view, "flint" refers specifically to the form of quartz or cherts that occurs in chalk or limestone. Similarly, "common chert" (sometimes referred to simply as "cherts"), occurs only in limestone.
Knapping flint involves carefully striking or pushing flakes from the stone being worked. This can be done by simply hitting the piece of flint with another rock (known as hard hammering) or using a "soft hammer" made of antler, wood or similar material (known as soft hammering). In contrast to directly striking the flint with another rock, a chisel made of metal, bone, wood or rock can be used to shape the flint. The final common method of removing flakes is 'pressure flaking'. Pressure flaking involves 'pushing' flakes off the piece being worked by the application of force to a precise point on a flint edge. Pressure flaking is usually done in the final stages to achieve the desired sharp edge, point, or to work the shape of, for example, notches in an arrowhead where it fixes to the shaft of the arrow.
Techniques used in flint–knapping
First, you need a heavy stone to hammer with and this can be any dense, weighty stone such as granite or any hard stone heavy enough to crack flint. This is known as a hammer stone. You should choose a stone that does not easily chip and fracture to reduce the risk of injury. Use the hammer stone to strike large flakes from the flint you are working on. The stone you are working is technically known as the "core". Strike the core with the hammer stone to remove the cortex from the core. This usually knocks flakes off the core and it is these flakes that are worked into tools or weapons. To begin removing flakes with a hammer stone, you need to know a little more about how flint fractures:
Interestingly enough, primitive man managed to make excellent stone tools and weapons with no knowledge of the science behind the process, however, understanding a little of what is going on will increase your chances of success rather than using trial–and–error techniques. The stones used for flint–knapping, (flints, cherts, obsidians, etc.) basically all fracture in the same way and this is called a conchoidal fracture. Force applied to the core sends shockwaves from the point of impact over the surface of the core, rather like ripples spreading out in a pond. However, the shockwaves also travel through the stone, so as the force spreads outward it also travels inward. The overall shockwave is cone shaped, with the apex at the point of impact and the base of the cone somewhere inside the core. This is technically called a "Hertzian Cone" or "The Cone of force".
The optimum scientific angle for this is 130 degrees to the direction of the point of impact of the hammer stone.
If you strike the core stone in the centre (unless you apply terrific force, which is dangerous), you will not detach a workable flake. The secret is to angle the blow near the edge of the core so only part of the cone of force passes through the core. It sounds all very precise and scientific, but in practice, you will soon master the knack and easily detach a workable flake of flint from the core. (See diagram below.)
To remove a flake of flint, find a place on the core where two faces meets at 90° or less so the cone of force works in your favour. This is known as the "platform". Rather than trying to hit the core at the right angle, it is easier to tilt the platform so you can hit vertically down on it to detach the flake as shown in the diagram below:
Controlling the shape of the flake
A little planning will help you to detach a flake suitable for your needs. Flakes follow the contours of the ridges in the core, so if you want a thin, straight flake to make a knife blade for instance, chose a face on the core as in "1" in the diagram below. If you want a broader, flatter flake to use for scraping, to shape into a spear head or arrowhead, chose a contour as in "2" in the diagram and if you want a long, curved flake to use for gouging, for example, chose a face on the core as in "3" in the diagram. You can see that by carefully studying the core you can detach flakes roughly in the shape of the final tool or weapon you desire; this will save a lot of time shaping the flake later.
The hammer stone
Choosing the right hammer stone is as essential as choosing a good piece of core stone to work. It is useful to find different hammer stones of different sizes and hardness's, depending on the hardness and size of the core being worked. If you are working obsidian, you need a softer hammer stone. Harder stones take more out of the core and leave larger "bulbs" on the flake. A harder hammer stone can quickly wreck a good core by taking these deeper dents out of it. A soft hammer stone may not work at all on harder materials like flint, cherts or jasper. Judging the hardness of the hammer stone comes with practice. Hammer stones are usually round to egg shaped and range in size from a chicken egg to larger than your fist.
Hard hammering is the technique used for reducing the size of the core or detaching a flake from the core. Despite its name, hard hammering is not whacking down on the core with all you might, it is more like a short, sharp tap. This, again, comes with experience.
Soft hammering thins and shapes the flakes removed during hard hammering; it is also the most difficult technique to master.
The hammer (known as a billet), in this part of the process is made of antler, hard wood or copper. The soft hammer is used to remove irregularities, to thin the flake, giving the flake its rough form ready for the final finishing using a technique called "pressure flaking". Soft Hammering is so–called because the hammer used is softer than the material being worked. Prehistoric man used antler or hard woods. Many modern "flint knappers" use copper hammers, but you are unlikely to have one with you in a survival situation and hardwood, such as the wood of fruit trees, works just as well as anything else.
When selecting antler for billets, choose a thick portion from the base or crown, where the antler attaches to the animal's skull. After the antler has been cut off, look at the cross–section. Most antlers will have a ring of dense material surrounding a porous interior. The less porous the interior the better for the purposes of knapping. Almost any hardwood can be used as a billet; beech, oak, mahogany and wood from many fruit trees, all work well. If you are in a survival situation, without a knife or commando saw, you will have to search for a broken piece of hardwood and shape it with a sharp edge of flint until you have made your first stone knife. Survival is largely down to common sense and invention!
The skill in working hard, glass–like stone with a soft hammer relies on finesse and technique, rather than on brute force and ignorance. When the soft hammer strikes the edge of the piece being worked, the edge flexes a fraction and a small part of it breaks off. A flake removed from an arrowhead with a soft hammer will have a slight lip on its underside. This lip is only formed by the flexing of the stone's edge and is one of the clues archaeologists can use to determine what sort of tools were being made at a site and how they were made — just from the debris left behind!
There are no set rules for soft hammering; you just have to find out what works. Getting this right is not easy, so be patient and experiment until you succeed. Sit comfortably and hold the piece being worked by sandwiching it between your thumb and first three fingers, resting on your knee or thigh. Take a firm grasp but do not grip too hard as this will tire your fingers and send more shockwaves through your hand.
Hold the piece approximately horizontal and strike down with the billet in an arc. Strike at roughly the same angle as the edge of the stone being worked so you chip off a small flake. Try to hit the edge of the stone, not too deep in, to remove flakes one at a time. You want a broad point of contact between the billet and the stone being worked. Use a fast, firm swing and you should snap a large flat flake off the piece and it will be sitting balanced on your middle finger. If you do not succeed, take your time, study the stone and try to work out why you were unsuccessful. Usually, the beginner strikes too deep into the stone, or doesn't hit hard and accurately enough.
Every time you have removed a series of flakes from an edge, it is essential that you grind that edge down very dull again so that the stone can withstand the impact of the next series of percussions or the jagged edge will collapse and the entire piece of work will break apart. This is the most important feature of flint–knapping. It is accomplished by grinding the edge of your flint in a sawing motion against another flattish sort of stone of slightly lesser hardness. The result is a dependable platform able to take the extreme rigors of further percussion. If not done properly, you will never be successful at producing anything more than fragments
Bear in mind:
Pressure flaking techniques
Pressure flaking gives the tool its final form and sharpens (and re–sharpens) the cutting edge. It can be used, for example, to make the grooves in an axe head to take the shaft. The piece being worked is held in one hand (usually your left hand if you are right handed, reverse if you are left handed) and the pressure flaker is held in the other. Because the flakes being removed come away from the underside of the stone, it is advisable to hold the stone in a piece of leather or other material to protect your hand from cuts.
Pressure flaking requires that a force be built up on the edge, the thin edge of the bi–face will crush if you do not prepare the platform. Do this by using the flaker, or another soft stone, to grind along the edge in the area where you want to remove the flake. The new edge will be able to hold long enough for the inward pressure you exert on it to build up, allowing the flake to be driven off. The flake will come off from the underside of the piece being worked. Remember, never to remove two flakes from the same area without first grinding along the edge to make a new platform.
To pressure flake, place a pointed tool on the edge of the stone and apply an inward pressure to the tool, focusing energy toward the palm, not away from it as with percussion (usually at a more severe angle of forty–five degrees). You will be working in the opposite direction than with soft hammering and you will be working on the face you can see when holding it.
This pressure will remove a small, thin flake from the stone. The slower and longer you apply pressure, the longer your flake will be. Longer flakes are desirable, as they continue to reduce the thickness more effectively. Up to 90% of your work may be pressure flaking and only 10% percussion, so be patient and work with attention to detail.
Do not forget to continue abrading the edge after EVERY series of flakes. Remember not to make two flakes in the same place without abrading. The closer you get to the finished product, the less heavily you will have to abrade, as you are working towards the final product — a delicate, razor sharp edge or point.
The flaker was traditionally antler although many contemporary knappers prefer thick copper wire mounted in some sort of handle. Unlike hard and soft hammer percussion, where finesse rather than force is used, pressure flaking literally pushes the flakes off. Depending on the material being used, this can require the application of considerable force. The point you are working on will already be bi–facially worked and have a sharp edge.
To make a modern practice pressure flaker
The pressure flaker should be 1.5 cm (0.6 inches) by 30 cm (2 inches) wooden dowel, made of any strong and flexible hard wood, never from softwood. It needs a sharpened copper nail set tightly in a hole in one end. Steel, iron, brass and bronze are too hard to grip the stone and do not work for pressure flaking, they will crush your work rather than shape it. Aluminium is too soft and brittle. The copper nail or wire should be no less than 12 gauge (2.05 mm) in thickness, sharpened to a dull point and should stick out no more than 1.5 cm (0.6) inches from its holder because copper is soft and can bend if too long. You will have to sharpen the pressure flaker fairly often.
This large and heavy stone bowl was found in a late 2nd century well in the UK. It is cut from a block of fine grained red sandstone whose source is thought to be around Bishops Lydiard in south Somerset, UK. It was presumably used for mashing food or grinding flour.
Flintknapped or flaked stone tools have a distinctive rippled appearance because of the way they are made by detaching flakes. Archaeologists also find stone tools that have a polished, smooth surface. These are called ground stone tools because that's how they were made (or more precisely, how they were finished). Ground stone implements can be quite diverse, ranging from bowls, pipes and lamps to knives, points and axes. It is useful to know the technique for making a crude stone ground bowl. For example, it can be used to capture water and as a drinking vessel. It can also be used as a mortar and pestle for grinding grain, seeds and roots to make crude flour.
Ground stone tools are not usually made out of the same type of rocks as knapped tools. Granites, quartzites and basalts, which are not nearly as nice to knap as finer grained cherts and natural glasses, can be made into serviceable tools by pecking and grinding. Sandstone and soapstone (steatite or talc–schist) can be shaped into a variety of forms, including cups bowls, or pipes. The Inuit and their prehistoric ancestors are famous for their work in soapstone, as were the Aztecs and people on the Indian subcontinent. Slate is also a common workable stone. It can be ground into flat, sharp, cutting and piercing tools.
Making ground stone tools
Pecking: This technique is just what it sounds like. The hammer stone (which must be harder than the stone being worked), is used to pound or 'peck' the stone into the desired shape. It's not as elegant or quick as knapping but the result is not for sale, it's for survival, so go for crude and practical.
Use a tree stump as a support for the stone you are working. If you hold the stone in your hand, your hand will absorb a lot of the force that should be going into the tool. You are wasting energy. And if you use a rock as an anvil, you are likely to shatter your stone.
Grinding & Polishing
This is the step that gives ground stone tools or articles their name. An abrasive stone, such as a sandstone pebble, is used to rub smooth the stone you are working on. This is done on either a pecked or a knapped blank. Ground stone implements can be knapped into their rough shape first and then ground smooth. Slate works well for this. It's a little soft to make chipped stone implements out of but it fractures the same way as cherts or obsidian does, so slate chunks can be shaped by flaking. Slate can also be ground smooth and sharpened in the same way as one would sharpen a metal knife.