Flintknapping has been likened to chess � you think about what you are doing, you plan your strategies in advance, the masters think several moves ahead, and you must be familiar with the rules in order to play the game. To begin removing flakes with a hammerstone you will have to be familiar with these three rules:

1. Conchoidal Fracture

The stones we use for flintknapping, (flints, cherts, obsidian, etc) all exhibit a characteristic fracture when broken � called a conchoidal fracture. When you strike the surface of the stone you are applying a force to the surface. This force spreads out from the point of impact like ripples spreading out in a pond. The force is also directed into the stone, so as the force spreads outward it also travels inward. What is produced is a cone, with the pinnacle at the point of impact and the widest part somewhere inside the rock. This is called a Hertzian cone or the cone of force. If you do this in the middle of the stone, unless you hit it VERY hard the force will dissipate without detaching a flake. The trick is to angle the blow and apply it near the edge of the stone so that only part of the cone passes through the core. In practice, I find it easiest to keep the direction of the blow vertical, and tilt the core up or down to change the angle. Luckily for us, these cones always tend to be about the same shape so the angles don�t change and once you learn how to make the cone work for you you�ve got it made! The angle that the flake detaches is about 130 degrees to the direction of the strike.

2. Near 90 degree platforms

The platform is the part of the core you strike to remove a flake. To find a potential platform on a core you want to look for a place where two faces meet at an angle of 90 degrees or less. It can not be greater than 90 degrees because of the way you are going to use the cone of force to work for you. Its not that angles greater than 90 degrees behave differently, its just that its impossible to hit them at the correct angle to get the edge of the cone to cut through them and remove a flake. In the Spot the Platform diagram, the platform is shown horizontal and the striking direction is angled. In practice, it is easier to find a near 90 degree angle, and then tilt the core so that your striking angle is vertical, as is shown in the Make the Cone Do the Work illustration.

3. Flakes follow ridges

This rule is not essential to detaching a flake, but it is essential to controlling where your flakes travel and in planning how to remove them. When a flake is removed from a flat surface it will fan out. The resulting flake will be short and wide (see flake B in the diagram), and quite often will end in a hinge or step fracture (not good). A flake struck at the same angle and with the same force above a ridge left by previous flake removals will travel through the area of most mass, the ridge, and will tend to be longer and narrower (see flake A). Knowledge of this rule will be crucial to controlling the flakes you strike off. Flake C curves and forks as it follows first one ridge and then a second.

Selecting a good hammerstone can be just as important as selecting good stone to flake. Most knappers have several different hammerstones of different sizes and hardnesses, depending on the hardness and size of the core which is being worked. For example, you want a soft hammerstone when working obsidian. Harder stones create a larger bulb of percussion on the flake, which in turn leaves a larger 'dent' in the core. These big divots in a core can quickly wreck it. However, a soft hammerstone might not work at all on harder materials like cherts or jasper. Judging the hardness of your hammerstone will come with practice.

Hammerstones are usually round to egg shaped and range in size from a chicken egg to larger than your fist. Even larger ones have been found at prehistoric quarry sites, but most knappers today don't use hammerstones to quarry their own raw material. One of the most important qualities of a hammerstone is that it fit comfortably in your hand. I prefer egg-shaped hammerstones, using the little end as the striking end. You can find suitable stones in most creeks and rivers. Alternatively, look along railroad tracks. The grade of gravel used along railroads (in my part of the world, anyway) is often exactly what you are looking for.