Edge Tool Making 3 - Materials (NEW)

A relatively large number of edge tools survive from the Bronze Age - mainly axes and sickle blades.  These were usually cast in bronze, and alloy of copper and tin using stone moulds. Billhooks from this period are almost unknown, but a few small vine pruning hooks do survive. From the Iron Age until the present day the most common material for making edge tools has been iron, which with the additional of a small amount of carbon can form steel. This section thus looks at the history of iron and steel making.


Iron rusts easily in the presence of water and oxygen to form iron oxides. Most iron ores are of a similar compostion, and can be located amongst other rocks by their reddish brown colour. To produce iron from its ore it is necessary to seperate it from the oxygen, a process known as smelting (chemically it is known as reduction), and the method of doing this was probably discovered by accident during the Bronze Age, as the process of obtaining copper and tin from their ores is similar.


The ore is first broken into small pieces and baked to remove any water. It is then placed into a furnace with fuel and pieces of limestone which act as a flux. As the fuel burns heat is produced and the rocks start to melt. An excess of carbon combines with the oxygen in the ore to produce CO (carbon monoxide) which produces more heat creating CO2 (carbon dioxide) - the process continues until all the fuel has burnt and all the oxygen has seperated from the iron, leaving liquid iron with a covering of molten slag which contains many of the impurities. The above description is only a brief outline of the basics of the process, the success of which depends on the quality of the ore, an abundance of good fuel and the skill of the ironworker - plus a good handful of luck. A small bloomery could produce an ingot of iron of about 20kg, which could be further refined to produce about 10kg of usable wrought iron or steel. Today large industrial processes produce batches of many tons at a time.


The following abstract on steel and tool making strategies and techniques is taken from the PDF file accomanying the Davistown Museum’s Exhibition  The Art of the Edge Tool.


1. Natural Steel: 1900 BC – 1930 AD

Natural steel was made in direct process bloomeries as occasional nodules of steel (+/- 0.5% carbon content (cc)) entrained in wrought iron loups, by altering the fuel to ore ratio in the smelting process, producing heterogeneous blooms of malleable iron (0.08 to 0.2% cc) and/or natural steel (0.2 to 0.5 cc and higher) or by carburizing bar or sheet iron submerged in a charcoal fire. Manganese laced rock ores (e.g. from Styria in Austria or from the Weald in Sussex, England) facilitated natural steel production; as a slag constituent, manganese lowered the melting temperature of slag, facilitating the more uniform uptake of carbon in the smelted iron. The first documented production of natural steel occurred at the height of the Bronze Age, 1900 BC, by the Chalybeans, using the self-fluxing iron sands from the south shores of the Black Sea. Occasional production of bloomery derived natural steel edge tools continued in isolated rural areas of Europe and North America into the early 20th century.


2. German Steel: 1350 - 1900

German steel was produced by decarburizing blast furnace derived cast iron in a finery furnace, and after 1835, in a puddling furnace. German steel tools are often molded, forged, or cast entirely of steel as exemplified by trade and felling axes without an inserted (welded) steel bit. Such tools were a precursor of modern cast steel axes and rolled cast steel timber framing tools; German steel shared the world market for steel with English blister and crucible steel until the mid-19th century.


3. Blister Steel: 1650 - 1900

Blister steel was produced by carburizing wrought iron bar stock in a sandstone cementation furnace that protected the ore from contact with burning fuel. It was often refined by piling, hammering, and reforging, into higher quality shear or double shear steel or broken up and remelted in crucibles to make cast steel. Blister steel was often used for "steeling" (welding on a steel cutting edge or bit) on axes and other edge tools


 4. Shear Steel: 1700 - 1900 

Shear steel was made from refined, reforged blister steel and was used for "steeling" high quality edge tools such as broad axes, adzes, and chisels, especially by American edge toolmakers who did not have access to, or did not want to purchase, expensive imported English cast steel. The use of shear steel was an alternative to imported English cast steel for making edge tools in America from the late 18th century to the mid-19th century.


5. Crucible Cast Steel: 1750 - 1930

Crucible cast steel is made from broken up pieced of blister steel bar stock, which is inserted into clay crucibles along with small quantities of carboniferous materials (e.g. charcoal powder). After melting at high temperatures, crucible cast steel was produced in 5 to 25 kg. batches and was considered the best steel available for edge tool, knife, razor, and watch spring production. Due to lack of heat resistant clay crucibles, extensive production of high quality crucible cast steel didn’t begin in the United States until after the Civil War.


6. Brescian Steel: 1350 - 1900?

Brescian Steel was a common Renaissance era strategy for making steel in southern Europe, for example, for the condottiers of the Italian city states. Wrought or malleable iron bar stock was submerged and thus carburized in a bath of molten pig iron. Brescian steel cannot be visually differentiated from German steel or puddled steel, both of which were produced from decarburizing pig iron.


7. Bulk Processed Steel: 1870 onwards

After the American Civil War, a number of new strategies were invented for producing large quantities of steel, especially low carbon steel, required by the rapid growth of the industrial age and its factory system of mass production. The first important innovation was Henry Bessemer’s single step hot air blast process, followed by several variations of the Siemens-Martin open hearth furnace and electric arc furnaces. For edge tool production, the electric arc furnace supplanted, then replaced, crucible cast steel in the early decades of the 20th century.

Until the availability of cheap carbon steels from the mid 19th century onwards, the principal material for making billhooks was wrought iron, a tough but relatively soft material, which was used for the body of the blade, to which was welded a steel cutting edge. Despite the time taken to forge weld the two parts together, this was far cheaper than using steel alone, and also gave the maker the ability to forge the blade more easily and to better manage the subsequent hardening and tempering process.