Blacksmiths work with "black" metals, typically iron. The black color comes from fire scale, a layer of oxides that forms on the surface of the metal during heating. The term 'smith' originates from the word 'smite', which means 'to hit'. Thus, a blacksmith is a person who smites black metal.

Blacksmiths work by heating pieces of wrought iron or steel until the metal becomes soft enough to be shaped with hand tools, such as a hammer, anvil and chisel. Heating is accomplished by the use of a forge fueled by propane, natural gas, coal, charcoal, or coke.

Modern blacksmiths may also employ an oxyacetylene or similar blowtorch for more localized heating. Color is important for indicating the temperature and workability of the metal: As iron is heated to increasing temperatures, it first glows red, then orange, yellow, and finally white; then it melts. The ideal heat for most forging is the bright yellow-orange color appropriately known as a "forging heat." Because they must be able to see the glowing color of the metal, many blacksmiths work in dim, low-light conditions.

The techniques of a blacksmith may be roughly divided into forging (sometimes called "sculpting"), welding, heat treating, and finishing.

Forging

Forging is also referred to as sculpting because it is the process of shaping metal. Forging is different from machining in that material is not removed by these . (exception of punching and cutting); rather the iron is hammered into shape. There are five basic operations or techniques employed in forging: drawing, shrinking, bending, upsetting, and punching.

These operations generally employ hammer and anvil at a minimum, but smiths will also make use of other tools and techniques to accommodate odd-sized or repetitive jobs.

Drawing

Drawing lengthens the metal by reducing one or both of the other two dimensions. As the depth is reduced, the width narrowed, or both the piece is lengthened or "drawn out".

As an example of drawing, a smith making a wood chisel might flatten a square bar of steel, lengthening the metal, reducing its depth but keeping its width consistent.

Drawing does not have to be uniform. A taper can result as in making a wedge or the woodworking chisel blade. If tapered in two dimensions a point results.

Drawing can be accomplished with a variety of tools and methods. Two typical methods using only hammer and anvil would be: hammering on the anvil horn, and hammering on the anvil face using the cross peen of a hammer.

Another method for drawing is to use a tool called a fuller, or the peen of the hammer to hasten the drawing out of a thick piece of metal. The technique is called fullering from the tool. Fullering consists of hammering a series of indentations (with corresponding ridges) perpendicular to the long section of the piece being drawn. The resulting effect will be to look somewhat like waves along the top of the piece. Then the hammer is turned over to use the flat face and the tops of the ridges are hammered down level with the bottoms of the indentations. This forces the metal to grow in length (and width if left unchecked) much faster than just hammering with the flat face of the hammer.

Shrinking

Shrinking, while similar to upsetting, is essentially the opposite process as drawing. As the edge of a flat piece is curved,—as in the making of a bowl shape—the edge will become wavy as the material bunches up in a shorter radius. At this point the wavy portion is heated and the waves are gently pounded flat to conform to the desired shape. If you were to compare the edge of the new shape to the original piece, you would discover that the material is thicker than before. This change in thickness is due to the excess material that formed the waves being pushed into a uniform edge that has a smaller radius than before.

Bending

Heating steel to an yellow/orange heat allows bending as if was hard plastacene: it takes significant but not Herculean effort. Bending can be done with the hammer over the horn or edge of the anvil or by inserting the work into one of the holes in the top of the anvil and swinging the free end to one side. Bends can be dressed and tightened or widened by hammering them over the appropriately-shaped part of the anvil.

Upsetting

Upsetting is the process of making metal thicker in one dimension through shortening in the other. One form is by heating the end of a rod and then hammering on it as one would drive a nail: the rod gets shorter, and the hot part widens. An alternative to hammering on the hot end would be to place the hot end on the anvil and hammer on the cold end.

Punching

Punching may be done to create a decorative pattern, or to make a hole. For example, in preparation for making a hammerhead, a smith would punch a hole in a heavy bar or rod for the hammer handle. Punching is not limited to depressions and holes. It also includes cutting, or slitting and drifting: these are done with a chisel.

Combining Processes

The five basic forging processes are often combined to produce and refine the shapes necessary for finished products. For example to fashion a cross-peen hammer head, a smith would start with a bar roughly the diameter of the hammer face, the handle hole would be punched and drifted (widened by inserting or passing a larger tool through it), the head would be cut (punched, but with a wedge), the peen would be drawn to a wedge, and the face would be dressed by upsetting.

In the example of making a chisel, as it lengthened by drawing it would also tend to spread in width, so a smith would frequently turn the chisel-to-be on its side and hammer it back down -- upsetting it -- to check the spread and keep the metal at the correct width for the project.

As another example, if a smith needed to put a 90-degree bend in a bar and wanted a sharp corner on the outside of the bend, the smith would begin by hammering an unsupported end to make the curved bend. Then, to "fatten up" the outside radius of the bend, one or both arms of the bend would need to be pushed back into the bend to fill the outer radius of the curve. So the smith would hammer the ends of the stock down into the bend, 'upsetting' it at the point of the bend. The smith would then dress the bend by drawing the sides of the bend to keep it the correct thickness. The hammering would continue—upsetting and then drawing—until the curve had been properly shaped. In the primary operation was the bend, but the drawing and upsetting are done to refine the shape.

Welding

Welding is the joining of metal of the same or similar kind of metal

A modern blacksmith has a range of options and tools to accomplish this. The basic types of welding commonly employed in a modern shop include traditional forge welding as well as modern methods, including oxyacetylene and arc welding.

In forge welding the pieces to be welded are heated to what is generally referred to as "welding heat". For mild steel most smiths judge this temperature by color: the metal will glow an intense yellow or white. At this temperature the steel is near molten .

Any foreign material in the weld, such as the oxides or "scale" that typically form in the fire, can weaken it and potentially cause it to fail. Thus the mating surfaces to be joined must be kept clean. To this end a smith will make sure the fire is a reducing fire: a fire where at the heart there is a great deal of heat and very little oxygen. The smith will also carefully shape the mating faces so that as they are brought together foreign material is squeezed out as the metal is joined. To clean the faces, protect them from oxidation, and provide a medium to carry foreign material out of the weld the smith will use flux -- typically powdered borax, silica sand, or both.

The smith will first clean the parts to be joined with a wire brush, then put them in the fire to heat. With a mix of drawing and upsetting the faces will be shaped so that when finally brought together the center of the weld will connect first and the connection spread outward under the hammer blows, pushing the flux and foreign material out.

The dressed metal goes back in the fire, is brought near to welding heat, removed from the fire, brushed, flux is applied, and it is returned to the fire. The smith now watches carefully to avoid overheating the metal. There is some challenge to this, because in order to see the color of the metal it must be removed from the fire, and this exposes the metal to air, which can cause it to oxidize rapidly. So the smith might probe into the fire with a bit of steel wire, prodding lightly at the mating faces. When the end of the wire sticks the metal is at the right temperature (a small weld has formed where the wire touches the mating face so it sticks).

Now the smith moves with rapid purpose. The metal is taken from the fire and quickly brought to the anvil, the mating faces are brought together, the hammer lightly applying a few taps to bring the mating faces into complete contact and squeeze out the flux, and finally returned to the fire again.

The weld was begun with the taps, but often the joint is weak and incomplete, so the smith will again heat the joint to welding temperature and work the weld with light blows to "set" the weld and finally to dress it to the shape.

Finishing

Depending on the intended use of the piece a blacksmith may finish it in a number of ways:

• A simple Jig (a tool) that the smith might only use a few times in the shop it may get the minimum of finishing: a rap on the anvil to break off scale and a brushing with a wire brush.
• Files can be employed to bring a piece to final shape, remove burrs and sharp edges, and smooth the surface.
• The wire brush either as a hand tool or power tool can further smooth and brighten a surface.
• Grinding stones, abrasive paper, and emery wheels can further shape, smooth and polish the surface.
• There are a range of treatments and finishes to inhibit oxidation of the metal and enhance or change the appearance of the piece. An experienced smith selects the finish based on the metal and intended use of the item.
• Finishes include but are not limited to: paint, varnish, bluing, browning, oil, and wax.