What materials to knap ?
First men have mainly knapped flint, but not only when flint was not available.
If almost any rock can be broken provided you hit it hard enough, all rocks cannot be turned into tools.
The ideal rock should have two essential characteristics :
• A sufficient hardness so that its active edge resists usage
• Physical properties allowing the production of controlled shape flakes, ie shaping the tool according to one's needs
Hardness
Hardness of a rock is usually measured with Moh's scale ranging from 1: very soft (Talc) to 10: extremely hard (Diamond).
Flint has a hardness close to 8, superior to forged steel's !
Physical properties
Rocks should not be cleaved or foliated (such as slate) and could ideally be flaked in any direction. Fracture should ideally be conchoidal (shaped as a shell), should allow the production of flakes and should leave a sharp edge.
Rocks lacking one or more of this characteristics can be shaped by pecking or grinding, such as serpentines, in order to make a neolithic axe for example.
Traditional materials
silex
Knapping quality
Hardness: 7
Description
Colors, hardness and knapping qualities may vary a lot depending on its source. Black opaque in northern France, it is honey-like and translucent in Touraine, beige-brown in Orléans, and multi-colored ringed in Bergerac. Note the presence of a chalky layer (cortex), absent on marine flint ...
Poor quality flints can often be improved by heating (a whole night in the ashes of a wooden fire)
jaspe
Knapping quality
Hardness: 7
Description
Always beautifully colored (yellow, tan, red, often veined) and very easy to work with, it is an ideal material for pressure flaking.
Even if often mixed with flint (the african bloc here is pure) and if certain blocks of flint main contain sub-cortical areas of jasper, blocks of pure jasper remain quite rare.
Main french source: Fontmaure
obsidienne
Knapping quality
Hardness: 5
Description
Ideal material, this volcanic glass is both easy to cut and horribly sharp: WATCH YOUR FINGERS!
Black, red, green, sometimes speckled, obsidian is also very reactive to pressure. One may however prefer the black, less tender and less fragile than red obsidian.
Almost inexistent in France, except in the minerals stores, it mailny comes from Mexico, Turkey, Italy or North America.
quartz hyalin
Knapping quality
Hardness: 7
Description
The quartz resembles glass in appearance, but the resemblance stops there!
Terribly difficult to work with, quartz produces chips that can not be controlled easily and often make step fractures.
The Neanderthals have however produced some nice quartz bifaces and some modern tailors still try it to duplicate these tools, as a challenge perhaps?
granit
Knapping quality
Hardness: 6
Description
Granit pebbles, due to their hardness and shape, make excellent hammerstones. They also may be turned into choppers, but fracture waves propagate quite badly: forget bifaces and pressure work !
quartzite
Knapping quality
Hardness: 7
Description
Often roundish, yellowish or beige, it is ideally used as a hard hammer for flint knapping.
Its relatively coarse grain makes it difficult to obtain flakes or blades, as well as fine pressure work, but it is an ideal material to start with hard percussion.
The quartzite is very abundant: mainly in the famous "graves" vineyards of Bordeaux.
gres
Knapping quality
Hardness: 7
Description
Made of compacted sand grains more or less fine, sandstone pebbles make good abraders or hard-soft hammers.
Poor knapping quality, similar to the quartzite, sandstone only allow larger flakes to be driven off the core, but can be worked by hammering and pecking and thus give the beginner knapper beautiful replicas of North African bifaces, small polished axes .. or Lascaux lamps!
Very common, especially in the South of France, the sandstone is quite usefull both as a tool than as knapping material.
basalte
Knapping quality
Hardness: 5.5
Description
Black and heavy rocks, quite widespread, basalts contain little silica and are poor candidates for knapping. They make however good strikers!
The fracture is rough, but the production of large fragments or edges allows the creation of choppers, and rustic bifaces.
Without better ones this is like river pebbles: an opportunist material
serpentine
Knapping quality
Hardness: 5
Description
Nice rock with green (hence the sknakish name) and blue veins, it belongs to the "greenstone" family which our ancestors used to make beautiful polished axes.
Almost not flakable by percussion or pressure, serpentine is carved by hammering or pecking its surface.
Common in mountainous areas, it serves as a dike on the beaches of the french island of Ré!
Polished, it has a fabulous finish.
Modern materials
The modern flintknapper may also one day, by game or necessity try thses less accademical materials out, whose properties are sometimes similar to hard rocks ones.
cristal
Knapping quality
Hardness: 7
Description
Although identical in appearance to glass, it's crystal (the crystal here fitts optical satellites).
Made by masters, it is an expensive material (unless you broke a vase !), but with exceptional qualities!
Chips as well as obsidian while being harder, crystal offers a sharp edge, each shard being a scalpel.
The result looks like quartz, but with no knapping drawback.
fibre optique
Knapping quality
Hardness: 5
Description
A truly modern material it is!
Ships as plates, sometimes pre-shaped in the form of arrowheads. Excellent for pressure flaking.
Its sometimes bright colors and the iridescent sheen of its surface have great success in Northern America, available from many sites. May be too modern for some.
verre
Knapping quality
Hardness: 6
Description
This is the poor man's obsidian and often the first material used by beginners (the famous beer bottle bottom).
Extremely easy to work by pressure, glass is much softer than obsidian .. but about as sharp: WATCH YOUR FINGERS!
Colored glass will make pretty arrowheads ... The displayed arrow point was made from a 5mm window glass by Cayoo.
agathe
Knapping quality
Hardness: 6.5
Description
Polished slices of agata found in minerals stores can have the most excellent as well as the poorest quality for pressure flaking once heat treated.
Prefer small pieces (the size of an average arrowhead) with a thickness of at least 5 mm and a minimum of crystals in the center (unlike the here displayed slice).
faience
Knapping quality
Hardness: 5
Description
Sink spalls, plates or even china are good candidates to knapping and respond very well to pressure or soft percussion, depending on the thickness of pieces.
These materials, more flexible and easier to work than stone are very abundant and are ideal when out of real flint.
carrelage
Knapping quality
Hardness: 6
Description
More or less hard and therefore difficult to work, tiles have a fairly pronounced conchoidal fracture reminding of the roughest flints.
According to their finesse and hardness, tiles will respond well to pressure (small chips possible) or to soft percussion.
Due to their shape, tiles are dedicated to arrowheads or small laurel leaves (here displayed).
Though easily found, tiles have a majoor drawback: its flat faces, a nightmare for knappers.