All European iron age cultures from as early as 500b.c. use forging as a primary manner of working iron or steel into functional shapes. Other basic tools and their use (filing, grinding, chiseling, punching, polishing,...) are all also with certain variations universally used. Medieval and Renaissance iron and steel blades used in knives and swords vary widely in material, quality, and design. but most construction techniques were known to all bladesmiths more or less proficiently. For instance while most iron using cultures learned to forge weld capably, several stand out for their complex development of the pattern welding technique. Certain areas would use fullering tools to forge a groove in the center of a sword blade while others would grind the swords fuller.
The purity and trace alloying elements of iron and steel vary depending on location and smelting. Raw materials used to make different iron items would be bog iron, bloom iron, wrought iron, cast iron, or steel of various carbon contents. Depending on the location and era some few smiths might produce their own raw materials from ore, bog iron, and rarely meteorite but for the most part iron and steel would be purchased or imported from a smelter. Iron and steel account for significant amounts of trade throughout the Middle Ages and Renaissance. The medieval European foundry/smelter was a brick or clay stack with ore and fuel (usually charcoal) stacked in layers and fired. The stack relied on air draft to actually melt and convert the ore into a combination of bloom iron or cast iron depending on the abundance of carbonizing materials (charcoal, dung...) in the smelter, and in atmosphere. These materials were then converted to wrought iron, then into blister steel or pattern welded steel.
Pattern welding was used widely in Europe throughout the Middle ages and later The technique itself accomplishes several things. It is a method of purifying the iron by working internal impurities (slag, undesirable alloying elements) to the surface of the billet where they will burn off in the fire. Pattern welding also allows a smith to combine smaller pieces of wrought iron and steel into a large enough bar to make a sword or large blade with. It can also allow the smith to control the overall carbon content of a billet by welding together two or more alloys of steel with differing carbon content into a billet of enough layers to allow the migration of the carbon at welding and forging heat which will tend to equalize the carbon and thus the hardness evenly through the billet. However, not all early blades had a hard carburized edge, of a group of La Tene (Celtic) Period (500-50 BC) blades examined by Radomir Pleiner (1993) only about 60% were medium to high carbon steel in one or both edges, the rest were wrought iron or very mild steel. Even this early smiths were building up most blades from multiple rods by twist welding them and fold welding as well. In better quality blades produced during the early middle ages hard, higher carbon billets were often used to form the blade edge while softer, low carbon steel billets or wrought iron, which would be more shock resistant were used for the core, sides or back of the blade. Quench hardening was widely used by Roman smiths and later throughout Europe. Swords with different styles of blade or hilt waxed and waned in popularity with location and era. Even when most swords were being built of a common style variance would occur. Even if only in the form of a few atypical works. Knives, axes and other iron implements were usually technically comparable to swords of their era.
Coal was not used prevalently as a fuel source for metalworking until the industrial revolution. Most coal found in any quantity on or near the surface of the earth is high in 8a~ output during burning and thus very inferior fuel. Wood however was relatively plentiful and charcoal is excellent fuel. Thus hardwood charcoal is the likely candidate for any medieval smiths fuel.
The basic tools needed for bladesmithing are: a forge, hammer, tongs and an anvil. A box of hardwood ash for annealing. A quench tank filled with oil or brine. Soapstone. Something to forge, simple carbon steel is best to start with and may be salvaged from a couple of readily available sources. Excellent alloys to start with are 1095, 5160, and O1 and may be found in old leaf springs (5160, 1095) and files ( 1095, O1 ). Once you have done one or two blades it only makes sense to use new steel as it is cheap compared to the time you will have invested in any single project.
Forging blades is a skill needing only a few simple tools and a great deal of subtlety in their use. Blades are forged for only a few reasons, to allow the smith to adjust a rectangular bar into a rough form of the final blade thus saving time during the second shaping, operations of grinding or filing and to refine the grain of the steel into a fine structure in the whole blade and to "pack" the edge (edge packing is of debatable effectiveness).
First, we will start with stock of a suitable size for the blade to be forged, width of the blank should be about 20% less than the finished forging. Length can be as long as is comfortable to hold. Mark out the tang area with soapstone. Heat and forge the shoulder of the blade/tang. Switch ends, heat and forge the tip profile, then forge the blades flats (using the same number of blows on each face to stress the blade uniformly) in however many heats are required (if done below bright red heat this is referred to as "packing" the edge crystals). Hammer the edge to a minimum thickness of 1/8" to 5/32" to prevent loss of carbon in the finished edge. Switch ends again, heat and forge the tang itself and cut any excess off. Now heat the full length of the blade evenly to above the upper critical point (around 1550 degrees Fahrenheit), tap it straight if needed and place on a non flammable surface to air cool. This step evens out the internal stresses in the length of the blade and is called "normalizing". After normalizing the blade reheat the entire length to above critical temp again and bury the blade in the box of hardwood ash, this will allow the steel to cool slowly to 1000 degrees F. or less (anneal) enough to form large grains of pearlite in which form it may be filed to shape and drilled for rivets. Once annealed the blade is ground and filed to nearly its anal shape, leaving the edge about 1/32" thick to prevent decarburization during hardening. When the blade is shaped, fit to its guard and drilled for the handle rivets it i.~ ready to harden, The blade is held in the forge and heated to its critical temperature (one way to tell critical temperature is by tapping the blade with a magnet, when the magnet stops sticking the blade is at the correct temperature) it is then immediately quenched edge first into the 160 degree F. automatic transmission fluid and rapidly agitated along its length until less than 400 degrees F. and allowed to air cool to room temp. If the blade is held at hardening temp too long the edge will lose more carbon and undesirable grain growth will occur in the entire blade. After the oil quench the oil will need to be washed off with a little soap and water and the blade can then be stress relieved either by heating in an oven at 400 degree F. for two hours or longer. Or by sanding the slag off until the steel is visible and selectively heating with a propane torch or in the forge (drawing temper by hand must be done carefully, the blade will suffer greatly from accidental overheating) to the colors indicated on the tempering, chart.
420 deg F. - Faint Yellow - knife/sword edge
430 deg F. - Very Pale Yellow - knife/sword edge
460 deg F. - Straw Yellow - knife/sword edge
500 deg F. - Brown Yellow - axes
530 deg F. - Light Purple -large knife or sword tip.
560 deg F. - Full Blue - blade spine and tang.
640 deg F. - Light blue - way too hot for any cutting edge, try again.
Once stress relieved (tempered) the blade is ready for assembly with the hilt. A word about safety, this art is greatly rewarding but never forget that it involves things that can burn you or your dwelling grind away bits of you, and a finished product that can cut or stab you. Use your head. Use your safety equipment and learn about the correct way to use your shop equipment. Shop equipment is expensive but worth the investment if you want to get any volume of good work done. Try to get set up with a gas forge, 2"x 72" belt sander and a drill press at a minimum, fill in other tools later.
To summarize:
Forge the blade shoulder, tip, profile, flats, tang.
Normalize, heat to above upper critical temp. and air cool.
Anneal, heat to upper critical temp. and bury in ash to slowly cool.
Shape with hand tools and fit to hilt parts.
Harden, heat to upper critical temp. and quench in 160 deg F. automatic
transmission fluid ( 130 deg F. heat treat oil is better).
Temper, heat to 400 deg F and hold 2 hr. to relieve internal stress.
Finish and assemble blade.
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