Using Steel for Sculpture, by Andrew Werby

An alt sculpture FAQ addressing the following topics: Steel in sculpture, Available types, Cutting, Bending, Hardening and tempering, Forming sheet, The forge, Cold attachment, Soldering, Brazing, Welding, Oxy/acetylene welding, Arc Welding, TIG welding, MIG welding, Grinding, Rust, Paint, Galvanization,Vitreous enamelling,Patinas, Safety considerations.


Over the course of the last 50 years, the use of steel for fine art sculpture has become common, although it was virtually unknown before the turn of the century. But its advantages- durability, malleability, and relative cheapness- have caused many sculptors to make it their primary material. It lends itself to large-scale work, but rewards hand detailing as well. Various parts - or the entirety- of the process can be contracted out to industrial fabrication companies, or the whole thing can be done in the artist's studio. As well as being a sculptural medium itself, steel is basic to our industrial world, and is an invaluable material for constructing armatures, supports, reinforcements. frames, jigs, fixtures, machines, and devices to further ones efforts in other media. So it behooves every sculptor, specialization notwithstanding, to attain a basic familiarity with steel-working techniques.


Steel is available in many cross-sectional shapes, such as "u"-shaped channel, "L"-shaped "angle-iron", "I" beams, flat "strap", rod, "rebar", pipe, tube (round, square, and rectangular), wire, and sheet. Past 3/16 inch in thickness, sheet steel is called "plate"., and is often used for sculpture. Bar stock includes round, square, hex, and flat, in various thicknesses from 1/8" on up. There are also quite a few different formulations of steel, the main types being "mild" steel, which is the kind most commonly used, tool steel, which contains more carbon and is thus susceptible to hardening and tempering, and stainless steel, which, in addition to its rust-resistance is quite a bit harder and tougher than most unhardened steels. It can also be readily purchased as sheet material in "gauges" or thicknesses from thin (28 gauge) to heavy (12 gauge and up). Steel often comes "galvanized" or zinc-coated. This makes it impervious to rust, but interferes with welding, producing toxic zinc smoke when heated. Steel is often obtained as scrap material of unknown properties. One way to tell tool steel from mild steel is to grind on some; tool steel will produce a "rooster-tail" of sparks due to its carbon content, while mild steel produces relatively few.

Different sorts of steel products may be cut in various ways, depending on the material and its intended use. There are cold cutting techniques and hot ones. Heavy mild steel beams, for instance, are usually cut using a horizontal bandsaw, "cold saw" (a water or oil-cooled circular saw), abrasive cut-off saw, or reciprocating power hacksaw, but they may also be cut with an oxy-acetylene cutting torch. This literally burns its way through the metal with a blast of pure oxygen once it reaches a certain heat. It only works on steel, though; for free-form cutting in other metals (or in steel) with greater precision a "plasma cutter" is needed. These are machines similar to arc-welders that liquefy a small patch of metal with a gas-shielded arc, then blow it out of the way with a blast of dehumidified compressed air. Lasers make a still cleaner cut, although they are still too expensive for most artists to consider buying for themselves. Abrasive water-jet machines are in a similar category. Still, if a project warrants it, there are laser-cutting and water-jet firms that will take on custom work. One can also cut steel with reciprocating saws, or with a bandsaw if it can be run slowly enough. For cutting thin sheets, saws tend to be less useful, since two teeth must be able to engage the work at all times or they will break off. For this, a range of shears are used, ranging from the stationary Beverly shear to a range of scissor-like tin-snips, as well as portable power shears and "nibblers". There are also stationary rod-cutters which can handle mild steel up to 1" diameter and bolt-cutters for cutting smaller stock. Stainless steel is cut using the same equipment, but special bi-metal blades for reciprocating and band saws help in cutting the tougher material. But lacking these expensive tools, much can be done with a high-quality hand-held hacksaw, with the work held in a vise.

Mild steel may be bent cold; it will take a considerable amount of deformation without failing, especially if "annealed" previously. This means heating it to red heat and cooling it as slowly as possible. For small projects, a metal can filled with vermiculite or perlite is helpful. (Non-ferrous metals usually anneal the opposite way, by being heated and then cooled quickly.) Annealing is especially important when dealing with tool steel, since it can become extremely hard and brittle through heat treatment. But this hardness is what makes steel springy, or able to hold a sharp edge. An oxy/acetylene torch may also be used to heat the specific area to be bent, since red-hot (or hotter) steel bends quite readily.

In order to harden tool- steel, it is heated to "cherry-red", then quickly quenched. Some steels prefer water-quenching, others require oil-quenching to avoid cracking. But fully-hardened steel is too brittle for most uses, so another operation, "tempering", is called for to reduce the hardness to a controlled degree. To do this, the hardened piece of steel is cleaned off so bright metal is showing, then it is heated until the "oxidation colors" precede one another across the surface. Each of these colors-light blue (hottest), blue, purple, peacock, bronze, deep straw, straw, and faint straw (coolest)- corresponds to a different temperature between about 400 and 640 degrees F, and hence a different hardness. When the desired degree of hardness is attained at the part of the tool that requires it, the steel is quenched to preserve it. The edge of a chisel, for instance, is generally tempered to a dark bronze color, while springs are tempered to their characteristic blue.

Any part of a tool that is to be stuck with a hammer, like the back end of a cold chisel, can't be left hard, or it will shatter dangerously in use. When steel is red-hot, even a heavy piece can be bent. At a light yellow heat (just before it burns) it becomes soft, almost clay-like in consistency. At this stage, it may be bent easily, or hammered into shape. The basic tool used is the anvil, which can be used with various accessories called "hardies". These are shaped pieces of steel with tapered square tangs which fit in the square hole in the anvil surface, and help in forming the hot metal. The hot steel can also be pierced, chiseled, or deformed using special punches, chisels, and hammers. A red heat is also fine for a final "burnishing"- a process of hammering to give a polish or texture to the surface. Heavy bending can be done more easily using a "post" vise. This is a heavy vise with an iron leg (the post) which reaches the ground, so one can do a lot of heavy hammering on the hot iron, without transferring the force of the blows to the bench. Using blacksmiths' bending forks, hot steel bar stock secured in the post vise can often be bent more easily than at the anvil.

Metalsmithing stakes and hammers are also used for forming sheet steel. The end grain of a wooden stump may also be used as an anvil for "dishing" sheet steel. Various cast iron forms are also available, to assist in reshaping sheet or bar stock. While some of these are expensive and difficult to obtain, one can get started with the inexpensive tools sold for auto-body repair. Other tools for hammering hot iron include the power hammer (with upper and lower dies that do the work of hammer and anvil) and the treadle hammer. The former is machine powered, with an electric motor or air, so it can greatly amplify the strength of the user. The latter also assists in hammering, relying on the leg strength of the user. It is useful for precise blows with a variety of interchangable "top tools." A tool called an "English wheel" is sometimes used for creating smooth compound curves in sheet (as in auto fenders)- one feeds a sheet between wheels, which can be either convex or concave, set on screws which can adjust for greater or less tension.

Small pieces can be heated with a torch for bending or forging- the "rosebud" tip on an oxy-acetylene outfit works well, although a cutting torch (without the blast of oxygen) will also work- but for larger ones a forge is very helpful. These are basically refractory containers which burn fuel using forced air to attain extra heat. Coal, coke, or gas (either natural gas or propane) are used, depending on what's available. The air supply, from a bellows or pressure blower, is introduced from below the firebed in the case of solid-fuel forges, or is mixed with gas prior to the ignition point in a gas forge. Some forge designs entrain air passively using a Venturi, eliminating the need for blowers. Whatever design you use, fine control of the airflow is essential, since sometimes you want the fire as hot as hot as possible as for forge welding, and sometimes it should be low, as for annealing.

One of the attractions of steel is the ease with which pieces of steel can be joined together. There are quite a few methods of doing this, both cold and hot. For cold attachment of steel to steel, a range of fasteners are used; either bolts, which are quite strong and permit easy disassembly, or screws which may be tapped into the metal,facilitating assembly from one side only. Rivets, which are usually set by backing up the heads on one side with a tool, while mushrooming the other side with a hammer, make a secure and permanent attachment that can also be decorative. "Pop" rivets, which are set from one side by a lever-action tool, can be quite effective for light sheet metal attachments. While adhesives can be used to put steel together, they are mostly used for attaching other materials to steel. For this to work, it helps to rough up the surface with sandpaper and degrease with acetone before applying the adhesive. Flexible adhesives work better than rigid ones on steel, since the metal's expansion and contraction with changes in temperature will tend to break a rigid bond.

Although welding is the primary attachment method used by sculptors in steel, it can also be joined using a lower-melting metal between the steel parts. This has the advantage of causing less heat distortion, since the parts being joined are not brought to as high a temperature as required by welding, where the steel parts themselves must be partially melted. Lead-tin solders and the newer lead-free solders may be used, with the appropriate fluxes. Except for light wire joints, which can be heated sufficiently with a soldering iron, a torch is used to heat the fluxed steel parts (not the solder) until the solder melts upon application and flows smoothly into the joint. The joint must be absolutely clean, or this will not work. Low-temperature soldering is used to join galvanized metal, the zinc coating of which would burn off in toxic clouds if hotter techniques were used. Jeweler's silver solder can also be used on steel, but it works at a much higher temperature than the lead or tin-based solders, requires a different flux, usually a white borax paste, and is very particular that the joints be well-fitted, without any gaps. There are various proprietary solders in between these two types, often with a small percentage of silver, which are not quite as strong as the high-silver solders but fill gaps better and melt at a lower temperature. These are called "Silver Bearing Solders".

Another technique which can be used is called "brazing". The hot flame of an oxy-acetylene torch is needed to melt brass or bronze rod onto hot steel, but it is an effective and quick way of joining steel parts which has decorative potential. The rod- I prefer to use silicon bronze rod for its strength and low fume emission- is dipped while hot into a can of powdered borax flux, and emerges with a flux coating. When the coated part of the rod is consumed, it must be re-dipped, or the bronze won't adhere to the steel. This method is not so particular about fit and cleanliness, although these things won't hurt in any case.

Welding, as I mentioned, is the prime method of putting pieces of steel together to make sculpture. There are five major techniques used; forge welding, oxy-acetylene welding, stick welding, TIG welding, and MIG welding. If the operator is skilled, any of these techniques can produce good results in a variety of situations. Forge welding is the original technique, developed by blacksmiths thousands of years ago. It is done by bringing two pieces of steel to white heat (one can see small sparks fly off as the material begins to burn). Then quickly, while the steel is still as hot as possible, they are pounded together with the hammer. Some blacksmiths use borax flux to help keep an oxide coat from separating the two pieces, others do without. Once this skill is mastered, it can be a very efficient way to weld. It requires no additional equipment besides a forge, hammer, and anvil, and can produce welds of special beauty.

The oxy-acetylene torch is a versatile tool, good for heating, brazing, and soldering; and it usually comes with a cutting attachment which permits steel to be cut fairly easily, if roughly. It is also a hazardous piece of equipment which must be treated with proper respect. Aside from the obvious hazard of burning oneself either directly or indirectly by touching hot objects, there is the danger of setting ones studio on fire or even causing an explosion by letting the volatile gas escape. The acetylene has been known to explode spontaneously if transported in an enclosed space like a car trunk, and it shouldn't be turned up past the low range (5) on the regulator. The bright light of the flame is bad for the eyes- although not as bad as the light caused by arc welding - so the appropriate goggles must be worn. For gas welding the goggles should be shade 5; for MIG, TIG, and stick welding a shade 10. The newer gold-coated lenses afford a little more visibility for the same-rated shade. For forging and forge welding, some people use only clear safety glasses- this is a minimum requirement, but the infra-red heat can cause eye damage- it's best to use didymium or shade 3 lenses. The metal itself will "pop" when overheated, so it is also essential to wear proper protective gear, traditionally including leather clothing, gloves, and cap. Avoid wearing synthetic fabrics. They tend to melt right into the skin, causing bad burns. The new flame-retardant cotton gear is lightweight and washable, and more pleasant to wear, especially in warm weather. The showers of sparks emitted by the welding process stay hot for quite a while, so one should avoid open pockets, etc. where they can fall in next to ones skin.

The torch-welding process involves adjusting the the oxy-acetylene torch so a tiny bright inner core flame, called an "oxidizing flame" appears, then taking a plain steel rod in ones other hand and feeding it into the drops of molten metal created on either side of the seam, joining them into one advancing puddle that knits the two sides together. The torch must be moved rhythmically back and forth as it advances in order to keep the two sides molten but not so hot they pop, and the feed metal must be added just right to unify the bead without sticking to the cooling metal. Although the process is fairly simple, it takes considerable practice to master. This and all welding processes work more easily on a flat and level surface; working on vertical and overhead surfaces is considerably more challenging.

The other three methods are variations on the process of arc-welding. In conventional arc-welding, or "stick" welding, a flux-coated rod is used as a combination of fill rod and electrode, establishing the arc by contact with the work, which has a "ground clamp" attached to it. By scratching the rod against the work- blindly, because the visor is totally dark until the arc illuminates things in its immediate vicinity- the circuit is established, and it continues when one pulls the tip of the rod away, due to the high- voltage current put out by the arc welder. (There are now auto-darkening helmets which go dark when the screen sense light, but they are still costly.)

One uses the rod in much the same way as the filler rod in oxy-acetylene welding, moving the tip side-to-side as the bead progresses. When the rod gets too short, it is replaced. When the weld has cooled, it must be hammered with a pick-like tool to remove the coating of flux that adheres to the surface of the weld. Rod comes in various types, but general- purpose rod is available that will work fairly well as AC and DC, straight polarity or reversing, and vertical as well as flat. Rod should be kept in a sealed container, since the flux layer is hydroscopic, and will absorb moisture from the air, causing it to crumble off the rod.

It is of utmost importance to protect ones eyes (and skin)from the rays generated by all the arc-welding processes, including MIG and TIG welding, and not to allow unshielded spectators to wander in, since blindness can result from a very short period of unprotected watching. Even the reflected arc can cause damage to bystanders. Portable screens of fireproof cloth are used if one must weld in any area to which unprotected people have access. There are also some considerable fumes emitted by the process, so some sort of ventilation is crucial for stick-welding indoors. Since one really can't see anything but the weld when doing this, fires can easily start unnoticed- so it's important to remove all flammable materials well away from where any welding takes place, because sparks ejected by the process can travel quite far and smoulder undetected for some time before bursting into flames. There is also a considerable hazard of electrocution, since one is dealing with heavy electricity at a very high voltage.

TIG (or Tungsten Inert Gas) welding is more controllable than stick-welding, since no flux is necessary, due to the protective nature of the inert gas being constantly blown into the weld area through the handpiece. The handle also contains a tungsten rod, which acts as the electrode but isn't consumed as the weld progresses. Instead, a filler rod is held in the hand, and is used in much the same manner as with oxy-acetylene. The current is regulated by a foot pedal, and a high-frequency spark removes the necessity to scratch- start, as in stick welding. The welds are generally cleaner, without flux inclusions or as much of the the spatter associated with stick-welding. One can weld a variety of materials with TIG, including stainless steel, mild steel, aluminum, bronze, and copper; some of which are very difficult to weld any other way. For most metals, argon gas is preferred, but it is expensive, and since mild steel isn't as particular as other metals, cheaper carbon dioxide can be used, either mixed with argon or straight. Although the whole process used to be called "heli-arc", because helium was the inert gas originally used, its annoying tendency to float away from the weld caused its replacement with heavier gasses. I suppose it would still be handy for welding upside-down.

While TIG offers the greatest degree of control, the most versatility between the types of material that can be handled, and the greatest facility for changing between them; another type of welding called MIG (for Metal Inert Gas) was developed to make possible quick and continuous welds that need not be interrupted for change of filler rods. Instead, a metal wire forms a consumable electrode, and it is forced into the weld mechanically when one activates it, giving the impression of squeezing liquid metal out of the handle and into the weld. The major problem is keeping up with the flow so as to make an even bead that doesn't get too thin or puddle up. Small MIG units are available that run on household electricity but are powerful enough to weld heavy sheetmetal. They are more expensive to set up than TIG, since an entire roll of wire must be purchased for each type of metal one wishes to weld. To save on expensive gas (although this wire isn't cheap), or to deal with difficult situations, such as a wind which blows the shielding gas away, a flux-cored wire is sometimes used in the mig-welder, for an effect much like stick welding.

Although some sculptors like the way the welds look, considering them a mark of process, others prefer to remove all traces of them by grinding and sanding, creating the appearance of a single piece of metal. On large-scale sculpture, the tool most commonly used for this is the right-angle grinder, which comes in a range of sizes for running grinding wheels, sanding disks, wire wheels and cup brushes in various diameters. Fitted with grinding wheels, this tool does the rough grinding, contacting the metal at a tangent to the outside edge of the wheel. I like the grinding wheels with a little flex to them; this allows a smoother contact over a wider surface than the more rigid wheels, reducing chatter and consequent irregularities. After the rough grinding, which unifies the surface but leaves it looking heavily scratched, sanding disks are used to smooth out the area and blend it in with the surrounding metal.

When using any tool with a rotating wheel, it's crucial to learn where to apply the wheel to the surface to be abraded, to avoid kickback. Even with care, kickback sometimes occurs. Injuries (and damage to the work) can also result from a piece being "grabbed" out of ones hands by a rotating wheel, and flung violently in a random direction. A new type of sanding disk has flaps of sandpaper arranged radially around the center. They are more expensive than the older type, which consist of a disk of sandpaper adhered to a rubber backing pad with semisolid "feathering adhesive", but they are worth the extra cost since they last longer and work better.

For fine grinding, a range of tungsten carbide bits are used in a straight shafted "die-grinder" which may be electrically or pneumatically powered. These are useful for cleaning up welds as well as for carving designs or letters onto the steel. For fine finishing, mounted abrasive points or sandpaper rolled in various shapes can be used in the same tool, mounted on special mandrels. Although most abrasive materials will work on steel, aluminum oxide (corundum) is the most popular, and is the abrasive usually found in grinding wheels and sandpaper products intended for steel work. All grinding, sanding, and wire-brushing operations with power tools require the use of well- fitted goggles with baffled vents to prevent the odd piece of grit being flung into ones eyes, as well as the major damage that can occur when a wheel flies apart at high speed, as can happen. Sparks from the grinding process can also cause fires, so make sure there are no flammable materials in the grinding area.

Rust is the enemy of steel. Left unchecked, rust can weaken, and will eventually destroy a steel sculpture, eating away at it until nothing is left but flakes of iron oxide. Fortunately, there are a number of possible surface treatments that will slow or stop this process. Or, if one likes the look of rusty metal but doesn't wish ones sculpture destroyed by oxidation, special steels like "Cor-ten" are available which form a layer of rust that stays on the surface but doesn't penetrate the steel. This layer actually protects the steel from further harm, making it possible to create permanent steel sculpture without paint or other coatings. But most steel, except stainless, requires some form of protection from the weather, if it is to be sited outdoors. It is possible to polish steel work to a high luster, but if it isn't protected from corrosion somehow this is wasted effort. If a high polish is desired, it is best to plate the piece with nickel, or nickel then chrome, gold, rhodium, or some other inert metal immediately after polishing.

The most commonly used coating for steel is paint. Although it requires periodic maintenance, it is the most cost-effective way to protect a piece of steel from the weather. Before painting,steel must be thouroughly cleaned and degreased, then a primer is used, which bonds to the steeland provides an optimum surface for paint application. Primers can be obtained with rust-conversion chemicals added, allowing one to paint a somewhat rusted surface without removing all traces of iron oxide. Once primed, almost any exterior-grade paint can be used on steel, but many sculptors prefer the lacquers developed for automotive use. These are generally sprayed on, not brushed. Most sculptors don't have access to the hot-dry rooms used for the original coatings on cars, but the products developed for repainting cars are designed to work without this treatment. As with any spray-painting, multiple light coats are better than heavy ones, which can cause drips, streaks, and other surface problems. It often helps to sand lightly between coats with fine (600 grit) wet-or-dry sandpaper; this evens things out and promotes adhesion between layers. Any spray-painting process releases toxic vapors and aerosolized material, so an appropriate respirator should be used. Additionally, spray mists can be explosive, and may be set off by electric motors and light sources, so a properly shielded spray booth is essential if large projects are contemplated. For interior sculpture, many of the finishes- lacquers, varnishes, and oils- used in woodworking can be useful Water-based varnish works well if a rust-inhibitor is added in proper proportions. The traditional blacksmithing finishes, oil-wax mixtures applied to hot metal, can also be very attractive, though they are less durable than varnish.

An extremely effective rust prevention treatment is hot-dip galvanization. This involves dipping the steel piece in a bath of molten zinc, which coats the metal smoothly, leaving a characteristic bright gray finish which can be quite attractive. For this to work, all hollow areas of the sculpture, including the interiors of tubular elements, must be vented to allow the zinc to enter and drain out. Most sculptors bring their work to an industrial facility specializing in this process, rather than trying to set it up in their studios. But for items that are unsuitable for dipping, zinc-rich paints have been developed which work almost as well. Any zinc-coated surface requires pickling with acid before paint is applied over it, or the paint will quickly peel off.

Another surface technique that works quite well for protecting steel is vitreous enamelling, although it isn't used much by sculptors because of the difficulties involved. Industrially, the process is used for coating bathtubs, sinks, and cookware. One first must use an undercoat of cobalt enamel; the dark blue coating with white specks often seen on cookware. After that, colored enamels (actually powdered glass) are applied to a gum covering the desired area, and the piece is fired in a kiln much like ceramics. An alternative that is easier to do is called powder-coating. This involves covering the piece with a layer of granules of plastic, which melt together into a smooth hard surface coating when placed in an oven. Though much the same as enamelling in principle, the temperatures used are much lower, although the resultant surface isn't as hard.

Steel sculpture may also be patinated, using various chemicals to change the surface color. Most of these color changes tend to vary over time, though, especially if the sculpture is sited outdoors. But for indoor pieces it is a viable choice, and the colors may be preserved for a longer period by waxing over the surface, either with automotive paste wax or one of the proprietary waxes designed for this ("Renaissance wax" is recommended as one of the best.) On a small scale, the range of colors available at gun shops can be useful, and patina companies like Birchwood Casey sell preformulated colors in larger quantities.

Since there are many dangerous processes involved in working with steel, the more instruction one can get the better off one will be. These remarks are meant only as a general introduction to this vast subject, and are in no sense a complete treatment of it. I may well have left out some crucial pieces of information that are necessary to know in order to do these things safely, and some of this information could be incorrect- so readers are strongly advised to get some hands-on instruction before attempting to do it themselves. I certainly will not accept reponsibility for any damage, injuries, or deaths that occur to those foolish enough to begin using these dangerous tools and techniques without finding out any more about it than what is in the brief synopsis given here. Fortunately, steel-working is a subject covered by most vocational education programs, as it is central to many industrial processes, so competent instruction is not difficult to find.

Copyright 1999, 2000 by Andrew Werby

Some places which deal with some aspect of steel sculpting:

If you need to buy smallish quantities of rod, bar, sheet, or other shapes in steel (also stainless steel, brass, copper, aluminum, or even titanium) click this link to Onlinemetals.com , which for a reasonable price will cut it and ship exactly what you need to your location.

Ron Reil's Forge Page: Explains how to build a simple propane-powered forge which doesn't require a blower.

The Eastwood Company sells a home powder-coating system geared for car customizers, but also useful for small-scale sculpture.

The Metal Web News: As well as linking to the Rec.crafts.metalworking FAQ, this site links diverse sources of information on metalworking processes available online.

ABANA: The Artist Blacksmith Association of North America sponsors workshops and other events, as well as maintaining an e-mail listserve and a useful collection of links and resources. It has chapters and conferences all over the US, and other countries have similar guilds with regular meetings. Going to these meetings is one way to begin increasing ones skills. Craft school courses is another. In Europe (and perhaps other places too) more formal apprenticeships are available for learning blacksmithing and metal sculpture.

The Metal Machining and Fabrication Directory: A good place to look for job-shops to contract out metal-related projects.

Parson's Airgas: One of many welding supply houses starting to come onto the internet.

Christopher Ray's website: An artist who used hot techniques to deal with metal directly.

Books:

I highly recommend an excellent book on steel-working, Alexander Weygers' "The Complete Modern Blacksmith" which compiles three separate books, :The Modern Blacksmith", The Making of Tools" and The Recycling and Reuse of Metals" You can read a review of it on (and even purchase a copy through) my online bookstore

Decorative Ironwork, by Dona Meilach, gives an overview of techniques that can be used with mild steel, with lavish illustrations including sculpture.

The Blacksmiths' Cookbook, by Francis Whitaker, has expert technical advice on traditional methods.