Hints and Tips

Materials

Heat treating raw material

• Heat treating makes detaching flakes easier from some kinds of stone. Flakes are longer and the flake scar is smoother, more lustrous and may even feel 'soapy'. The color of the stone may change on the outer surface (and sometimes internally too), usually to a redder or browner hue. But the stone also becomes weaker and more brittle.

• Rocks can blowup while being heat treated. This can happen at any time. Usually this isn't dangerous but it can be. Protect your kiln or oven, particularly if it has a glass viewing window, by putting the rocks in a metal container such as a covered roasting pan.

• When heat treating rock, first you must dry the rock or it will blow up, explode like bombs, as steam is suddenly released. An hour at 200 degrees F. has proved sufficient for preforms made from quartz, agate and chalcedony from the surface of the western Mojave desert. Other stone, particularly freshly quarried stone, may require more time to dry. This initial drying reduces moisture content but doesn't eliminate it entirely.

• Raise the temperature gradually. I have found, starting with room temperature preforms up to one inch thick, that an initial oven temperature of 150 degrees F. is OK. After an hour, I raise the temperature 50 degrees F. and hold it there for drying time. After drying, I raise the temperature 50 degrees F. each half hour.

• Lower the temperature gradually. I have found that up to 550 degrees F. just turning off the heat is safe ( I use my kitchen electric oven).

• Don't open the oven door until the temperature is below 150 degrees F. or thereabouts. You can check this by turning the oven on to 150 degrees F.; if the heating element or gas flame doesn't come on the temperature is still above 150.

• Not all rock improves with heat treating. Some will be ruined by it. If the heat treated rock's knapping properties don't change the temperature they reached may be too low. If the rock has broken or has little blister-like flakes comming off it (pot lids) it is ruined for knapping. One or more of the following is the likely cause: the temperature was too high, the holding time at max temperature was too long, the temperature rise or fall was too fast, the rock's thickness was too great, the rock was non-uniform or had flaws or impurities in it.

• Before heat treating a large batch of preforms made from unfamiliar stone, experiment with some of the debitage. Ovens, rock, and what they do when combined vary greatly.

• Three main things happen as rock is heated. First, moisture is driven out. Second, the rock expands. Third, chemical and/or structural changes occur.

• The faster you raise or lower the temperature the more stress occurs within the rock. This is due to rapid steam pressure buildup in rock still containing residual moisture (see above) and from unequal expansion or contraction due to uneven heating (the outside heats and cools before the inside).

• Non-uniform materials expand non-uniformly. Thus they are less likely to survive heat treating.

• Small pieces heat treat successfully because the forces acting within the rock are less than in a large mass.

• A thin flake survives better than a round nodule.

• A long thin flake survives better than a flat disk.

• A smooth surfaced piece survives better than one with angular scars and notched edges.

Poor quality raw materials

• Is it worthwhile to work poor quality material? In favor: it is cheap so you can practice new techniques or warm up at the beginning of a session. High quality material should be respected and never squandered. Against: it can be discouraging and cause you to develop a conservative, defensive approach to knapping that prevents utilizing the real potential in good quality materials. Beginners, and to some extent everyone, can get discouraged when pieces crumble unexpectedly.

• Very tough materials (high strength, low brittleness) such as porcelain, quartzite, and most basalt, among others, can only be worked into relatively crude tools.

Tools

Hammerstones

• A cobble of tough dense stone with a well rounded shape, such as a well tumbled creek or river stone, makes a good hammer stone. An elongated potato or egg shape gives a good feel in the hand and a definite striking end.

• Choose a hammer stone lighter than the rock mass you are detaching flakes from but heavier than the flakes you intend to detach.

Billet size and shape

• A large radius billet end contacts a broad area giving flatter flakes; a smaller radius and/or harder material billet gives a deeper bulb of percussion.

• Use a billet that is an appreciable percentage of the mass you are working, less than the total mass but more than the flake to be removed. Balancing these masses is the way to transfer energy from the billet to the piece most effectively.

Weight of billet

More weight for:

• Larger flakes

• Large preforms

• Large area of flake break surface

Less weight for:

• Smaller flakes

• Delicate, thin biface

• Brittle materials (for example: glass, obsidian, some heat treated stone)

Billet maintenance

• Dress the billet's striking surface to a smooth hemispherical end.

• A pitted billet face has two problems associated with it. First, the billet is effectively softer but not in a uniform, consistent or predictable way. Thus, results become less predictable. This is more noticeable as the piece needs more delicately controlled work such as secondary thinning. Second, the friction of the face against the platform (the piece edge) is variable in unpredictable ways. Thus, the point where flake detachment initiates is less predictable as is flake size.

Pressure flaker

• Pressure flakers were traditionally made from antler or bone. Most modern knappers use copper wire set in some kind of handle. Either works well but copper has the advantage that it is easier to obtain for most people, inexpensive (use #4 copper ground wire from a building supply store), and requires less frequent resharpening. The results are somewhat different since copper is generally harder and sharper than flakers made from antler or bone.

Technique

Edge preparation

• Prepare platform at or below center plane of the piece and at or below the rest of the adjacent working edge.

• Trim the edge to form the angle you need for the length and thickness flake to be removed. Close to 90 degrees for a long flake, less for shorter.

• Grind the razor edge before a billet strike. This strengthens it against shattering, which gives crushed areas and 'chatter'. On initial contact, the billet must skid across the edge some at first but catch after a bit. Too much grinding makes the edge too slippery and the billet can't catch and initiate the break. Too little and the billet catches right away initiating detachment before the inward force has developed which makes the desired long flake. You need to balance the strength and friction properties so that the desired size flake detaches.

• When grinding pressure flaking platforms aim for a 90 degree angle or slightly less to produce long flakes.

Holding the piece

• The piece must be prevented from moving to some degree during the blow. If it is allowed to freely move the blow must be harder which makes it more difficult to aim accurately. Often when the first strike fails to dislodge a flake it is only necessary to hold the piece more firmly against movement rather than hit it harder.

• Before striking, push the billet tip against the platform to help seat the piece in your grip. This can also aid accurate aim.

• When using a billet, hold the piece in a way that helps reduce the bending it will be subjected to by the blow.

• When using a billet, provide vibration dampening for the piece. This can be accomplished by laying it on a pad on your leg or by hand holding it touching a lot of its surface.

• When pressure flaking, beware of the 'death grip'. It causes rapid fatigue, finger joint damage, and broken flint.

• When pressure flaking, pay attention to where pressure is coming against the work both from your fingers on one side and the pad or support on the other. If the pad side presses mainly on the ends of the work your finger pressure and the flaking tool both are tending to bend the work in the same direction; it could break.

Aiming

• Aiming the billet is easier if you relax. A lot of loose wrist motion and less arm motion is better than the opposite. Follow through; don't try to stop the end of the stroke abruptly.

• Grip the billet with your thumb and three fingers. Lay your pointer or index finger along the top of the billet. This is especially helpful with small billets that must move fast.

• Touch, with the end of the billet, the place you are aiming at. Then draw back and strike.

• Keep your eye on the spot you want to hit, not on the moving billet.

• Get over your work. If you have a clear view of the intended spot you are aiming at you are more likely to hit it.

• For extra accuracy, immobilize your upper arm by bracing your elbow against your side.

• Practice, practice, practice.

• Relax.

Striking the piece

• Hammer stones require little effort on your part to detach a flake. Think in terms of guiding them rather than bashing. If you do bash, many large flakes will break and the flake scar will show more undulations.

• With hammer stones you strike the surface of the stone at something like a 60 degree angle (measured from the plane of the surface) inclined such that the blow tends to push the flake away from the main mass of stone. The angle can vary from 80 degrees to 45 degrees without much variation in the flake length.

• Hammer stones are used for hard hammer direct percussion. You strike the flat surface. Billets of antler, copper, wood, or a wide variety of other possible materials are sometimes used for hard hammer percussion but are mostly used for thinning flakes. Thinning is done by hitting the edge of the flake which has often been prepared. Pressure flakers are used for finishing. Pressure retouch is done on edges, similar to billet work, but is more precise.

• The angle of the billet relative to the center plane of the piece strongly influences how hard you need to swing. If the axis of the billet is in line with the piece all its mass is working. Striking with the side of the billet is the same as using a lighter billet.

• A small billet must be directed more into the piece and moved faster than a large billet for the same energy and detachment rate.

• Swing with an easy motion. Follow through, don't try to use your muscles as brakes.

• A lot of the billet's speed (and thus effectiveness) comes from wrist motion, sort of a snapping motion. But don't exaggerate this wrist snap motion.

• Hold the billet fairly loosely. A tight grip will prevent some of the important wrist motion.

• If the flake fails to release when you have hit it correctly, check your platform before hitting it again harder.

Some factors affecting flake length

• For long flakes, make nearly 90 degree platform angles.

• Long flakes need more energy delivered over a longer time to break more rock area. Force needs to be applied for enough time for the long break to travel the required distance. That's why softer, heavier billets work better for longer flakes; they have less bounce so the force lasts longer and more mass so it takes more time for a given force to push it away.

• Flakes from a gently convex surface run farther.

• Flakes that follow ridges travel farther.

• Supporting the flake to prevent it from breaking early by hinging away from the main mass it is being detached from increases flake length.

• In general, striking more into the mass of the piece, more nearly parallel to the direction of the center plane, results in longer flakes. But beware; if you strike too near parallel to the center plane you will get very short shattered flakes with multiple steps and hinges (chatter), or you may get a rising fracture that exits on top of the piece (cutting it in half), or the piece may just break in two.

Thinning strategies

• Initially, thinning is often done from platforms near the center plane following or utilizing relatively pronounced ridges. Secondary thinning is done from isolated platforms created well below the center plane, along convex surfaces with poorly defined ridges.

Recovering from Errors

• Broken pieces can sometimes be glued back together and finished. Super glue ( I use Duro brand ) works fairly well on obsidian and brittle heat treated stone. A fresh break needs no preparation other than removing chips and dust that interfere with a good fit. After gluing, wait until the next day or longer before continuing work on the piece. And don't expect miracles; be extra careful about stressing the piece.

Strategy

• Take advantage of natural platforms and ridges.

• While edging a piece, if you have an opportunity to take thinning flake do it.

• Concentrate work on thinning from the ends of the piece while it is still thick and the ends are still rounded. Once the piece is thinned significantly avoid striking the ends as much as possible. Energy (in the form of vibration) from the blow travels down the piece and becomes more concentrated where the piece narrows at the far end. Thus, the vibration amplitude increases and can break the end off the piece. Pressing the thin narrow end of the piece against your padded leg or otherwise holding it against an energy absorbing surface can greatly reduce breakage from 'end shock'.

• Thinning a piece requires that it loose thickness faster than it looses width and length. For this to happen flakes must travel past the middle of the piece. Thus, the center looses material from flakes removed from both edges.

• Small notched arrow heads are often broken during notching. Most modern knappers notch the piece after finishing everything else. But if you notch it earlier you save yourself some frustration if it breaks. If the broken piece is still long enough you may even get a second chance at notching it and finishing it up.

• Make every flake do the most possible work. You loose width with every flake so minimize their number.

The Inner Game

Psychology

• As you work the piece it gets more fragile. It's easy to get carried away while working on a piece, particularly in billeting. A little problem leads to a big mistake if you fail to change your rhythm and pace. It's so easy to just hit the piece again, harder, when a flake fails to release. Repeated rehitting breaks lots of good materials that would otherwise have survived to become good points or blades.

• Relax. Tension wears you out and decreases your accuracy and judgment.

• When unsure of what to do next, stop. Think about how to proceed, or take a break.

• Flintknapping is often frustrating. To counteract feeling discouraged, occasionally look at pieces you made previously. The good ones can reassure you that the frustration is worth it; the inept ones can remind you of how much you have progressed. Probably you will realize that your standard of what is a finished work have become much more demanding.

• Larger, longer, thinner pieces with a regular scar pattern are vastly more difficult to produce than seems reasonable from their easier counterpart.

• No matter how long you knap, you can continue to build skill. Flintknapping has no inherent limit.

• Be bold. The only way you can improve at a satisfying rate is to press the limits of your skill. You break some mediocre pieces this way, but when you succeed you produce better work and you learn.

Theories

• The Hertzian cone explains only the initial breakage as a flake begins to detach. It fails to explain most of the breakage path for many flakes.

• In general, you must go by experience, not theory, when knapping since no one has an adequate but simple explanation for what happens as fracture initiates and propagates.