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Some of the earliest roman buildings have elaborate gutter systems and catch basins used to collect rain water for drinking and household uses. The art of casting bronze has been in use for thousands of years. In my own interest in learning about the history of how copperworks makes its beautifull art class leaderheads and downspout brackets, I stumbled across a lot of information. This information has little practical value for the average potential A.B. Raingutters customer, and they are best to refer to the copper page or the accesories section. But... it's not like I'm typing this in line by line. Point-click-copy-paste. Dig it? I always was one to exhaust myself and anyone who would listen about the things that interest me.

Here is an example of a cast bronze product that I regularly use. Don Miller of Copperworks cast his own hardware using traditional methods. The result is a art quality item, stronger and longer lasting than anything else available. The detail of his work is unsurpased in the mainstream market. The cost is prohibitive to some, and for those who like the look, but lack the funds to spend $165.00 (installed ) per bracket, I have a middle ground line of sheet-metal brackets for both copper and aluminum raingutters.

As the fashioning and baking of clay into useful and beautiful objects was one of man's earliest discoveries and indeed may be said to come almost naturally to human fingers, clay moulds were probably employed for the earliest metal castings; a few wooden ones are also known. Open moulds no doubt came first; but as these can only produce articles that are flat on one face, the use of closed moulds must have followed soon afterwards. To cast copper successfully calls for special precautions, as it may give rise to sulphurous gases; molten copper also tends to pick up oxygen which can create unsound castings. Special openings or risers in the mould are therefore necessary, both for pouring the metal and to permit the escape of dirt and gases. The ancient coppersmith, however, was well aware of these difficulties and became very successful in overcoming them.

When a little tin or lead is added, even accidental amounts like i per cent, the production of sound castings becomes much easier; and this must have hastened the development of bronze as a definite alloy. Eventually their techniques became so sophisticated that bowls of almost incredible thinness, yet still perfect, were cast in this metal. At an early date great skill was acquired in fashioning double stone moulds which allowed repetition work. Sand castings, however, seem to have been less common.(3)

By one or other of these processes, all manner of things came into existence-palstaves, axes, bowls, tools of many kinds, weapons, celts, figurines, large vases and sacred vessels.

The Egyptians are commonly credited with inventing the lost wax or cire perdue method of casting metal. This was known too in China, but apparently only at a much later date. A. Lucas(4) describes the process:
'A model in beeswax was made of the object to be cast. This was coated with a suitable material to form the mould, probably clay or a clay mixture, and embedded in sand or earth which acted merely as a support. The hole was then heated and the wax melted and either burnt away or ran out through the hole or holes provided to receive the molten metal; the mould became hard and rigid, and ready for use. Then the molten metal was poured in and allowed to cool, after which the mould was broken away and the object given the necessary finishing touches with a chisel.' Cire perdue provided solid castings upon which a great refinement of ornament or detail could be worked. Hollow castings were also made: these required some kind of core which was held in place either without support or by wires or other devices.

Another casting method, ideal for repetition work, was to fashion clay around an article and then remove the coating in sections. These were next thinly coated with wax and carefully reassembled. Hot wax was poured in and the mould rotated until the required thickness of solidified wax was obtained upon the inner walls. The removal of the mould left a complete wax model which could then be embedded in a suitable moulding material for treatment as described earlier. The necessary air-vents and runners for the metal were fashioned in wax whilst additional ornamentation was frequently applied by means of dies.

By these various methods, metal shells and patterns of extreme delicacy were frequently obtained.

The process of beating thin copper sheets against a former, with or without the addition of special ornamentation or engraving, was also used by the ancient coppersmith to make a large variety of artistic objects.

Bronze is a hard, durable, metal alloy made by melting copper and tin in varying proportions. Bronze melts readily and is easily worked, molded and tooled. It doesn't rust when exposed to moisture, and it takes on a fine smooth finish. these properties along with it's ability to take on beautiful coloring makes it a valuable material to the artist. Once processed, blended and placed in the hands of an artist, the copper becomes an artistic statement for all time-the Bronze Sculpture.

The lost-wax method of bronze casting is at least 6,000 years old, dating back to ancient Greek, Roman and Near East cultures. Many of the old principals are used in today's lost wax process.

The earliest bronze works were solid. It was 2000 years later during the Akkadian period in Mesopotamia that artists learned how to cast hollow interiors. Now, the door was open to create larger works.

The lost wax bronze method developed continuosly, linking pre-history to present day artists.

Soon after the year 1000 AD masterpieces cast by lost wax appeared. From this time on, the method was used by all of the great sculptors, including Donatello (1386-1466) to Rodin (1861-1909) and Russell (1864-1926).

It was not until the late 1800's that any bronze casting was done in North America. Prior to this, artists had to travel to foundries in Munich or Paris to have their castings completed. Today some of the finest foundries in the world are here in the USA.

Bronzes are created from original sculptures from which master molds are created. It is from these molds that wax duplicates are created and it is through the lost wax method that a bronze is created. Many artists founder more than a single casting. They will created editions from 1 to 1000 units. Though the edition may be large, each sculpture is an original work of art. No two bronzes will be identical because of the nature of the process and the fact that a wax pattern will be hand worked by the artist or a trained artisan prior to investment and again after casting. This process gives each bronze individual value no matter how extensive the edition size.
BRIEF HISTORY OF BRONZE CASTING

Lost wax casting has been around for thousands of years, yet few people understand how the process actually works. Although mechanization has facilitated the lost wax process of bronze casting, the procedure is basically the same as that used by the Chinese when they first developed the process in the 2nd millennium BC.

First the artist creates an original sculpture out of any of number of media, including stone, wax, clay, wood and pottery. This image is coated with a silicone rubber molding material that makes two rubber mold halves (each rubber mold has a front and a back piece). A fiberglass outer shell is added to the back of each mold so it retains its shape and rigidity during subsequent uses. These molds are the only components that are ever re-used in the casting process. All other components are re-created for each casting. Once the molds are done, the insides are coated with layers of wax. The halves are then bound together and wax poured inside to complete the wax image being created. Once the wax has cooled, the mold is peeled away, yielding a wax image duplicating the original sculpture. This image must then be "touched -up" to remove any seam lines, scratches or other flaws, as well as to recreate any pattern or texturing that was lost or damaged when the wax was made. The quality of the finished bronze relies on a clean, high quality mold and an impeccably recreated wax image that is as near to perfect as possible.

The next step, "gating", is the application of a series of tubes and funnels that allow the molten bronze to flow through to the bottom of the ceramic shell and the hot gases to escape at the same time. These sprus are created by attaching wax rods to the finished wax form at strategically spaced locations.
After the gating is completed each wax form is dipped in a liquid ceramic silica-sand compound so it is completely coated inside and out. Holes called "patches" have been cut into the wax to allow an entrance to the inside of the form. The form is subsequently dipped 6 to 12 or more times over a period of several days until the desired shell thickness is achieved. Once these ceramic shells have dried thoroughly the pieces are placed into an autoclave and the wax is melted out (hence the term "lost wax"), to be reclaimed and used again. The shells are then cured in a kiln so they will withstand the temperature of the molten bronze being poured into them.

Bronze ingots are melted to a temperature of approximately 2000F and poured into the cured ceramic shells. As the sculpture cools the ceramic shell begins to pop away from the bronze. This shell will be completely broken away, using a hammer and chisel, before the superfluous metal materials are cut away. The casting is then sandblasted in preparation for metal finishing. Any pieces of a sculpture that were cast separately are welded back onto the sculpture and any seam lines or other imperfections are removed or "chased". Finally, any texturing that was lost or damaged in the casting or welding process is recreated and the sculpture is polished in preparation for application of the patina.

The different colored finishes that are possible on cast bronze sculptures are called patina's. The various colors, patterns and textures obtained in the patina process are achieved through a combined application of chemicals and heat, augmented by hand stippling, or spraying with an air brush, and sealed with lacquer and waxes.

Most bronzes are part of a "limited edition" containing a fixed number of castings. This edition number is decided by the artist, usually after the first piece has been cast, and individually stamped on each piece (i.e. 1/100) thus concluding the process of bronze sculpture production.

Home | The Artists | Casting Bronze | History of Bronze | About the Gallery
The history of the lost wax process dates back to before history itself approximately 6,000 years ago. The Latin word is sicerus, meaning "without wax" bronze real and true without a single imperfection. The French word is cireperdue meaning enduring prestige. The Egyptians or the people of Northern Asia considered bronze to be the metal of the Gods.

About 250,000 years before Christ, the first significant developments of humanity occurred. The old stone age man made an important discovery which set him apart from the other beasts of the forest and field. Fire and mans development for controlling it for his own purposes. For cooking purposes, pottery was developed thus discovering the refractory qualities of clay. Evidence seems to indicate that meat was packed in leaves and covered with clay to prevent charring. When the combustibles burned away the clay still remained. Thus the stage was set for the coming of casting bronze. Now they had fire to melt metals and clay for crucibles to hold it.

It is fabled that a native banked his fire one night with a copper bearing ore and in the morning noticed some gleaming beads in the ashes. Hammering of copper now was attempted. But, here man became exposed to his first fundamental lesson in metallurgy. The copper became harder under hammering and a new element for the prehistoric world was born. This was about 4500 BC. The first molds were open and made ins and. Then they developed open faces molds in clay to facilitate permanent and more reliable castings. The close ties between molding and ceramics brings archeologists to believe that some unknown genius to whom the world still is indebted probably originated as a potter. While etching on the design, prior to firing, it occurred to him that the piece would be more attractive and stable if made in metal. He shaved off the etched design and reduced it in size. Then with bees wax he brought it back up to the original size and re etched the design in the bees wax. Upon this wax-coated mold he then placed it in his kiln. Under the heat, the wax ran out. Then into the completed mold he poured alloy of copper and tin, known today as bronze. When the metal cooled the mold was broken away, revealing in metal the first lost wax.

Considering this early artisan's background of experience, his was an innovation of the greatest importance. No other process can be named by archeologists so crowded with deduction, engineering ability and ingenuity. When one considers the meager tools and education lost wax molding must be classed as an achievement equal to the invention of the wheel or the discovery of fire.

The oldest known casting in existence is a cast copper frog found in Mesopotamia probably cast about 3,200 B.C. Meanwhile, European civilizations were being born in Crete and Greece. Crete, which entered the age of metals around 3,000 B.C. developed a remarkable bronze casting industry, and the accent copper-rich island of Cyprus, are the earliest lands mentioned metalurgically. Cyprus is important because it is from here that copper derives its name. Copper was certainly the Cretan's most cherished possession which they call Cyperium metal. Under the Romans the name became coprum and later changed to copper.

As the molding and castings evolved into the complex designs of art, blisters and imperfections on the pure copper surface seemed inevitable. The achievement of a perfect vast seemed doomed. But an accident again ultimately came to the rescue. Finally, the truth began to dawn on the early founder. He discovered that ore containing impurities would produce perfect castings. So, the alloy of copper and tin was discovered.

Written evidence of early bronze castings also goes far back in history. It is mentioned and described at great length in the bible. A notable example is found in 1st Kings where one of the early bronze artisans Hiram of Tyre is introduced: "a craftsman in bronze, wise, adroit, and skillful" was summoned to work for King Soloman to work on the Lord's temple about 1066 B.C. He created a bronze pool 7 1/2 feet deep, 15 feet in diameter, and weighing 45 tons mounted on eight bronze life size oxen.

It was the Greeks in the 16th century who brought the bronze casting into perfection. They found marble static, fragile, and limiting. Bronze offered freedom, not being limited by their medium, they were free to express with no restraints on form or size. As a monument to the Art of Greek foundrymen was an enormous bronze statue of the Greek God Apollo. It is one of the seven ancient wonders of the world. Cast in sections and assembled it towered105 feet tall above the Harbor of Rhodes, one foot on each shore weighed some 360 tons and was equipped with a winding staircase.

Archeologists believe that the lost was method was used in America as early as 1200A.D. It could account fort the fine detail and complex forms of the Inca's earliest figurative jewelry, cast in pure gold.

Sculptors and foundrymen were ranked with nobility from the early times and held in high regard. Their technical secrets in the metallurgical field were carefully guarded. It was spiritual and they would leave the ultimate outcome of the pour to the gods. Performing ceremonies and blessing the molds before the pour to insure perfect castings so that their labor and talent were revealed in the bronze.

1. Original Sculpture

The original sculpture is created by the artist using clay, wax, or plastilina. Depending on size, sculpture can be cast as a whole or cut into pieces.

2. Creating the Molds and Wax.

A rubber mold is made directly onto the original sculpture. A plaser "mother mold" is made encasing the rubber. Molds are removed, reassembled, and filled with metled wax. The hardened wax is removed and carefully hand-finished to replicate the original.

5. Burning Out the Wax

The wax, with its heavy shell coating, is now steam heated, melting out all of the wax, leaving only a hollow shell. This is where the "lost wax" term applies.

6. Pouring the Bronze

While the bronze bars are heated to liquid form, shells are baked to a ceramic-like stone. Melted bronze is then poured into the hollow cavity within the shell.

9. Chasing the Bronze

Imperfections to the surface, as well as marks and scars left when removing the bars and funnel are repaired in a process called "chasing."

10. Assembling and Welding

The sculpture is reassembled and welded into correct position. Wleded seams are again "chased" by the artist until the bronze is identical to the original work.

3.Spruing the Wax

Wax rods are attached to the sculpture (called gates and sprues) in a manner resembling arteries. These gates lead to a wax funnel at one end of the rod.

4. Investing the Wax

Hardened wax is first dipped into a liquid "shell" vat. While still wet, it is slowly lowered into a dry silica-sand, forming a rigid shell. This process is repeated in layers, creating a hard plasterlike shell.

7. Revealing the Bronze

Once the bronze is cool, the shell if broken away with hammer and chisel. Bars and funnel are also removed at this time.

8. Sandblasting

Any remaining shell is removed by two stages of sand-blasting; first with coarse, then with fine sand.

11. Patiniation

The coloration of the bronze is achieved by applying heat and chemically controlled tarnishing to the metal. Chemicals can be applied, sprayed, or brushed on in various degrees of heat known as "applying the patina."
This description of the Lost Wax process has been extremely simplified and does not begin to address the many in between stages, complications, variations, and the exhausting endurance of hours, days, and months that elapse in the process of creating a single bronze.
1. Original Sculpture

The original sculpture is created by the artist using clay, wax, or plastilina. Depending on size, sculpture can be cast as a whole or cut into pieces.

2. Creating the Molds and Wax.

A rubber mold is made directly onto the original sculpture. A plaser "mother mold" is made encasing the rubber. Molds are removed, reassembled, and filled with metled wax. The hardened wax is removed and carefully hand-finished to replicate the original.

5. Burning Out the Wax

The wax, with its heavy shell coating, is now steam heated, melting out all of the wax, leaving only a hollow shell. This is where the "lost wax" term applies.

6. Pouring the Bronze

While the bronze bars are heated to liquid form, shells are baked to a ceramic-like stone. Melted bronze is then poured into the hollow cavity within the shell.

9. Chasing the Bronze

Imperfections to the surface, as well as marks and scars left when removing the bars and funnel are repaired in a process called "chasing."

10. Assembling and Welding

The sculpture is reassembled and welded into correct position. Wleded seams are again "chased" by the artist until the bronze is identical to the original work.

3.Spruing the Wax

Wax rods are attached to the sculpture (called gates and sprues) in a manner resembling arteries. These gates lead to a wax funnel at one end of the rod.

4. Investing the Wax

Hardened wax is first dipped into a liquid "shell" vat. While still wet, it is slowly lowered into a dry silica-sand, forming a rigid shell. This process is repeated in layers, creating a hard plasterlike shell.

7. Revealing the Bronze

Once the bronze is cool, the shell if broken away with hammer and chisel. Bars and funnel are also removed at this time.

8. Sandblasting

Any remaining shell is removed by two stages of sand-blasting; first with coarse, then with fine sand.

11. Patiniation

The coloration of the bronze is achieved by applying heat and chemically controlled tarnishing to the metal. Chemicals can be applied, sprayed, or brushed on in various degrees of heat known as "applying the patina."
This description of the Lost Wax process has been extremely simplified and does not begin to address the many in between stages, complications, variations, and the exhausting endurance of hours, days, and months that elapse in the process of creating a single bronze.

A Brief History of Bronze in Art

The creation of works of art in bronze is one of the most ancient and widespread art forms. For over 4,000 years, bronze has played an important role in art. Bronze tools revolutionized the arts of woodworking and stone working. This metal also served as a new medium for artists.

The use of bronze for statues, coins and decorative articles dates back to approximately 3000 B.C. Bronze working continued through the 10th and 11th centuries in China, India, Egypt, Greece, France, Germany and Italy.

Bronze was a prominent metal in Chinese art. The earliest Chinese works in any form are in bronze. There are numerous examples of bronze work from the 14th century B.C. Early Chinese bronzes are of great value for their aesthetic appeal, decoration, patina, beauty of form and for their documentary value as historical records. The lost-wax process was developed in China during the Shang Dynasty in 2000 B.C. Most Chinese bronzes were produced by the lost-wax method and inlay work was customary. Bronze figure casting began with Buddhism and starting in the Sun period (960-1279 A.D.), numerous bronze sculptures were created.

The Etruscans made extensive use of bronze and were highly skilled in its working. The Romans made considerable advances in the technical aspects of bronze casting - particularly the use of prefabricated parts and in methods of joining bronze castings. During the centuries between the fall of the Roman Empire and the first years of the Romanesque period (c. 1000 A.D.), stone was used more frequently than bronze for sculpture. The Carolinian Renaissance of the 9th century marked the return of bronze. In the 10th century, during the Ottoman Period, bronze was used extensively.

Bronze was primarily used for architectural features during the Renaissance in Italy. The future of bronze sculpture was greatly influenced in 1432 by Donatello's decision to cast his work of David in bronze. The statue of David was the first freestanding nude statue created since classical times. A school for bronze sculptors was established at Padua in the 15th century by followers of Donatello.

In France during the 16th century, bas-relief was the predominant form of bronze work. From 1400 to 1800 A.D., the Benin culture, which inhabited southern Nigeria, produced beautiful bronze ritual objects known as Benin bronzes. The 16th and 17th centuries were high points for bronze carving in west Africa. Bronze statuettes were abundant.

Gilt bronze was very popular in the late 17th and 18th centuries. In 1788, a process of founding with sand was invented in France which became as popular as the lost-wax method of hollow casting. In the 18th century, bronze sculpture was produced on a more modest scale. Antoine Louis Barye, a great animal sculptor, created some of the finest bronzes of the century.

The use of bronze in art declined during the 19th and 20th centuries. Direct carving became the preferred form in the early part of the 20th century.

Today, cast bronze is unchallenged in the fine arts as a medium especially for freestanding sculpture. The durability and lightness of bronze make it preferable to stone or wood in many types of work. Bronze sculpture offers a freedom of conception, which is impossible in stone.

Source: Matthews International Corp.

A Brief Explanation of the Lost Wax Process

Clay

The sculptor builds the clay to the desired form, usually over a wire armature, which supports the weight of the clay.

The Mold

A mold is made of the sculptor's clay original by applying a mold compound. Then, plaster is applied to support the rubber and avoid distortion when the clay is removed. The original clay is destroyed in the demolding process. The mold is a negative of the original clay, which was a positive. Three dimensional sculptures usually require multiple piece molds.

Wax Casting

200+ degree wax is poured into the assembled mold. When the wax is cool, the mold is carefully removed.

Wax Chasing

Seams, air bubbles and imperfections are removed from the wax using special tools to replicate the original work. This is called "chasing". The number in an edition is inscribed on the wax. The finished wax is a positive.

Gating and Spruing

The wax positive is gated with wax tubes, providing channels for the wax to be removed, and funnels called sprues are attached to receive the molten bronze. The piece is vented with wax to avoid air entrapment.

Ceramic Shell

The finished wax is dipped in a clay slurry which is called ceramic shell which picks up minute surface details on the wax. It is allowed to thoroughly dry and is dipped and dried about eight times. This can take up to eight days.

Lost Wax or Burn-out

The completed ceramic shell is inverted and heated. This causes the wax to melt out, thus becoming "lost". The shell is allowed to cool and is surrounded with supports to prevent breakage during bronze pour. The negative space in the shell will become the positive bronze casting.

Casting

Bronze is heated to 2250 degrees, and is poured into the cooled shell. After the bronze cools, the shell is broken away. The bronze is then blasted with tiny glass beads to remove all traces of ceramic shell. The gates and vents are sawed off, and the surface is repaired. Any parts removed to facilitate the bold process are welded back on.

Metal Chasing

Foundry personnel carefully chase the welded seams, gates and vents to closely resemble the artists' original surface. The finished metal is blasted again in preparation for patina.

Patina

Chemicals are sprayed or painted on the bronze, and they are heated with a torch. Different chemicals cause different effects and colors. When the patineur has achieved the desired affect, paste-wax applied and heated.

In the third millennium B.C., somewhere between the Black Sea and Persian Gulf, an artist crafted a vision in beeswax, covered it in liquid clay and cooked it in a fire. In the flames the wax was lost, replaced by empty space. Tin and copper - alloys of bronze - were gathered and heated. Once melted, the metal was poured into the cavity of the fire hardened clay. The metal cooled and the sculptor knocked the clay from the metal. The first bronze was cast.

Ancient "Lost Wax" bronze castings have withstood the centuries, visually telling the tale of past cultures, their religion and their social structures. For example, Chinese bronzes depicted ceremonial images; Indian and Egyptian castings symbolized deities; Africans cast images of nature; and the Greeks re-created the human Form. Many of the cultures have grown obsolete, religions have evolved and societies have changed. Elements of the "Lost Wax" process have been refined. Yet today, bronze casting is essentially the same as it was in 2,000 BC during the Akkadian period.

Modern sculptors who want their pieces cast in bronze depend upon a foundry. There, artisans skillfully apply the "Lost Wax" method to wood, stone, clay, plaster or any other kind of sculpture to transform it into bronze. Artworks Foundry, in Berkeley, CA, is a world renowned foundry that casts many prominent artists' work.

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THE RUBBER MOLD
The metamorphosis of a sculpture from the original medium into bronze begins with a rubber mold.

The original sculpture must remain stationary during the mold making process. To accomplish this, half of the sculpture is nestled into a base of soft plasticine clay, the other exposed half is painted evenly with a clear, viscous rubber. (Polyurethane rubber is best for single or small editions while larger editions require silicone rubber.) When the half painted with rubber dries, a protective and rock hard "mother mold" made of reinforced plaster is built around the pliable rubber. The sculpture is then turned over, and the process repeated. When the second side is complete, the mold is opened and the original removed from within. The rubber is rejoined with the other half, rendering an exact "negative" image of the sculpture in rubber.

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THE WAX POSITIVE
The original sculpture is now used exclusively as a reference point. From the "negative" rubber mold, a wax "positive" is created.

Wax is melted to about 210°F, poured into the mold and evenly coated or "slushed" inside. Slushing is repeated three times using cooler wax each time to avoid melting the previous coat. Under ideal conditions, the wax wall will be about 3/16" thick --- any less might create flow problems for the bronze; any more will result in a heavier than necessary sculpture. When the mold is opened and the rubber peeled away, an almost perfect wax reproduction is removed.
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WAX CHASING · SPRUING & GATING
"Wax chasing" is the delicate process of joining the wax pieces, removing seams and repairing imperfections with heated customized soldering irons or tools - dental tools are ideal. Artists are encouraged to visit the foundry at this point to sign and check the integrity of the wax.

After the wax is chased and approved by the artist, the piece is then advanced to "Spruing" or "Gating." The gates and sprues are also made of wax. They form the channels through which the melted bronze will travel to the artwork.
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"Vents" (thin wax sticks) and "Gates" (thicker wax sticks) are affixed to the wax reproduction with heated tools. Later in the casting process, the space occupied by sprues or gates become runways through which the metal flows and trapped gas escapes. Distribution of the bronze, low turbulence, ventilation and shrinkage are important considerations in the science of gating and spruing.
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INVESTING
"Investment" is the process of building a rock-hard shell around the wax sculpture. Later, when the wax has been melted out, the investment will serve as a mold for the molten bronze. For most of history, an investment consisting of plaster, sand and water was used to accomplish this task. In the last 15 years, a new technology called ceramic shell has become the industry standard. Artworks Foundry converted to a 100% ceramic shell system in 1995.

The ceramic shell technique begins by dipping the gated wax into vats of slurry followed immediately by a bath of sand. This process builds a very thin wall of silica around the wax. When repeated approximately 9 times, allowing for dry times in between dips, a hard shell about ½" thick forms around the wax.

Prior to the invention of ceramic shell, solid plaster investment was used. To invest by the solid plaster method, tar paper is loosely wrapped around the wax reproduction in the shape of a cylinder. The enclosed space surrounding the wax is then filled with a wet plaster/sand mixture. When the plaster hardens, the tar paper is removed and a solid plaster investment is ready for "de-wax."

Whether ceramic shell or plaster is used to make the shell, the wax is a "positive" which must disappear in order to create a cavity or "negative" for the bronze to fill. Thus the phrase "lost wax casting" comes from the process of the wax being melted or "lost" from the shell. Ceramic built shells are "de-waxed" in a high pressure steam chamber known as an autoclave; plaster invested shells are de-waxed in a kiln.
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THE POUR
A huge graphite crucible, fired by a furnace, is filled with bronze ingots that are melted. The metal begins to melt at 1700°F. Bronze "seizes" (stops flowing) when confronted with cold, which might occur if molten bronze was poured into a room temperature shell; therefore at the same time the bronze is being blasted by a natural gas furnace, the ceramic shell is heated in a kiln to approximately 1100°F.
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When the "Dance of the Pour" begins, the crucible is lifted by a crane out of the gas furnace. At the same time, the glowing ceramic shells are brought out of the kiln to the pour area. Two artisans operate the crane which holds the crucible in a "jacket." The artisan with the controls is the "lead pour," the artisan maintaining the crucible balance is known as the "deadman." A third member of the pour team pushes away dross and slag on the surface of the molten bronze.
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The entire pour is very fast and very precise; one crucible of bronze holds 400 lbs and can fill one or two large shells or ten or more small shells. The first pieces poured are those with thin walls and intricate details; requiring hot, fluid bronze to move throughout the channel system.

The alloy cast at Artworks is known as Silicon Bronze. The metal is made up of the following elements: COPPER 94.0%, MANGANESE 1.1%, SILICON 3.9%, TRACE ELEMENTS 1.0%. Silicon is an additive which helps the "flowability" of the bronze. It achieved widespread use during World War II when lead and tin were in short supply.
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DEVESTING
"Devesting" is the process during which the investment is removed from the metal. Approximately one hour after the pour, the piece is cool enough to handle. Skill and strength are combined with hammers and power chisels to knock the investment off the freshly solidified metal. The gates and sprues must also be removed with a high intensity electric arc that can cut through the bronze like butter. The final step is to sandblast the fine investment from the bronze. When clean, the sculpture advances to the metal shop…
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METAL CHASING & FINISHING
Like wax chasing, bronze must also be chased or cleaned to address the slight imperfections that may result from the casting or shell building process. On larger sculptures, where assembly of cast sections is required, chasing is essential to take down weld line formed by the joining of two planes.

Metal chasing usually starts with large electric or pneumatic grinders to remove the bulk of the unwanted metal. Then, more refined and smaller tools such as die and pencil grinders are used to re-create the artist's subtle surface texture.

Much as a house needs a wood frame to stand, many monumental bronzes require a stainless steel internal structure to support the bronze "skin." Most larger than life-size bronzes are analyzed by a structural engineer who recommends a support structure that can withstand earthquakes and high winds.
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PATINA
Patination is enhancement of bronze by the chemical application of color. Three water soluble compounds form the basis for most patinas: Ferric Nitrate produces reds and browns, Cupric Nitrate creates the greens and blues and Sulphurated Potash produces black.

Each foundry develops its own proprietary (and carefully guarded) patinas that result from a carefully orchestrated blend of different chemicals, pigments and application technique. A wide range of colors, both transparent and opaque are available to the experienced patineur. The final step is putting a thin coat of clear wax over the bronze to enhance and preserve the patina.
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The Legacy of Investment Casting
Investment casting, the process used at Hitchiner Manufacturing to produce intricately detailed near-net-shape castings, is one of the oldest and also the most modern of the metallurgical arts. Hitchiner employs the latest scientific advances in CAD-CAM design and manufacturing, automated systems, conveyorization, robotics, countergravity casting techniques and other innovations to produce the highest quality investment cast parts available today.

Hitchiner castings are at work in the fiery combustion chambers of jet aircraft, in the sub-zero vacuum of space, on the world's streets and highways and in a myriad of other applications. Yet, the root of this technology, the cire perdue or "lost wax" process dates back many thousands of years. The artists and sculptors of ancient Egypt and Mesopotamia, the Han Dynasty in China, and the Benin civilization in Africa used the lost wax method of casting to produce their intricately detailed artwork of copper, bronze and gold.

It is remarkable that the art of lost wax casting was so widely known in ancient times. It is not an easy process and calls for considerable skill in its execution. The Aztec gold-smiths of pre-Columbian Mexico used the lost wax process to create much of their elaborate jewelry. Unfortunately, few examples of this work survived the plunder of the conquistadors. Countless masterpieces were melted down into gold bars to enrich the Spanish treasury. The quality of the few pieces which have survived demonstrate a mastery of the process which must have taken many years of trial and error to develop. Accounts of the methods used are provided in the book by Friar Bernardino de Sahagun, who spent 60 years in an intensive study of Aztec Mexico. Each step in the process, which is described and illustrated in his writings, was told to him by the Indians themselves.

Some of the finest remaining examples of pre-Columbian Mexican casting were discovered in the 1930s at Monte Alban, the sacred mountain of the ancient Zapotecs near the city of Oaxaca. Many gold artifacts found there were decorated with wirework presumably made by dipping threads into melted wax and applying them to the beeswax pattern prior to casting.

In the city of Benin, now a part of Nigeria, brass smiths continue to produce lost wax castings using a method passed down through the ages from one generation to the next. A study of their methods provides a living example of the early history of the investment casting process.

The brass casters at Benin begin with a core of clay kneaded into a mass. They shape the clay into the approximate size and shape of the article to be made. These cores are then allowed to dry thoroughly in the sun for several days.

The brass smith creates a pattern for the casting by covering one of these cores with beeswax and carefully modeling it into the exact shape desired. Thus, each casting is a unique hand formed work. When the wax form is finished to the artist's satisfaction, it is covered in a thick coating of clay. Sometimes the cores are made to be self supporting, in other cases small pins are used to keep the core centered. The first layer of clay is applied as a very fine slip. Before the pattern is fully sealed in this coating, a thin roll of wax is added to form a channel into which the molten metal will be poured. Subsequent layers of a thicker clay are added, gradually investing (covering) the form completely, creating a mold. This mold is allowed to air dry thoroughly.

When a batch of molds have been created and are ready for casting. they are placed in a fire and heated so that the wax will melt and can be poured off. The clay molds are further heated to a point where they are sufficiently fired to permit the pouring of the molten metal without causing the shell to burst. Meanwhile, pieces of brass are melted in crucibles on a nearby forge fire. The fire on the force is stoked by a manually operated bellows.

Immediately prior to the pour, the molds are taken from the fire and placed upright in spaded earth. A crucible of metal is taken from the forge with long tongs and the molten brass is poured into the open mold. The brass smith holds a wooden stick in his other hand during the pour and places it on the edge of the crucible to help insure a smooth flow of metal into the shell. Soon after casting, the molds are broken open, the shell knocked off and the final object is cleaned, filed and polished. Benin lost wax castings can be found in museums throughout the world.

Shortly after the dark ages in Europe, the industrious sculptor and goldsmith, Benvenuto Cellini began to make use of the lost wax method of casting. He learned this process from the writings of the monk Theophilus Presbyter (circa 1100) whose Schedula Diversarum Artium is the earliest known foundry text. In Cellini's autobiography, considered to be one of the classics of literature, he describes in great detail the casting of his famous Perseus and the Head of Medusa. This three and a half ton statue was completed in 1554 and was unveiled at the Loggia dei Lanzi in Florence, Italy, where it stands to this day.

The investment casting process has been used in the arts by many civilizations for countless centuries. Not only was this process in use, but it was developed to a high degree of excellence, as is attested to by many beautiful and finely detailed statues, jewelry and artifacts from antiquity.

This technique was largely ignored by modern industry until the dawn of the twentieth century, when it was "rediscovered" by the dental profession for producing crowns and inlays. The first authenticated record of the use of investment castings in dentistry appears in a paper written by Dr. D. Philbrook of Council Bluffs, Iowa in 1897. However, the true significance of this process was not realized until the research of Dr. William H. Taggart of Chicago was published in 1907. Dr. Taggart not only developed and described a technique, he formulated a wax pattern compound of excellent properties, developed an investment material and even invented an air pressure casting machine.

During World War II, with urgent military demands overtaxing the machine tool industry, the art of investment casting provided a shortcut for producing near net shape precision parts and allowed the use of specialized alloys which could not be readily shaped by alternative methods. The investment casting process was found practical for many wartime needs--and during the postwar period it expanded into many commercial and industrial applications where complex metal parts were needed. It was in this period that the Hitchiner Manufacturing Company was founded at the Amoskeag Millyards of Manchester, NH.

The solid mold technique was first utilized because a technology to successfully remove the wax patterns from a shell without causing it to collapse, crack or burst had not yet been devised. In the solid mold technique, a wax sprue was placed in a steel casing and surrounded by a setting slurry. The drawbacks of the solid mold technique were extremely long pre-heat, size limitations and poor dimensional tolerances.

The first successful shell technology was the Mercast Process, which used solidified mercury as a pattern material. Mercury patterns were very heavy but extremely accurate. This was a very difficult process as all pattern production and shell building had to be done at temperatures below minus 39 degrees Celsius--the melting temperature of mercury! This process is no longer used due to high costs and the health hazards involved in handling this toxic element.

The first shell process utilizing wax patterns was developed in England and was known as the Investment X Process. This method resolved the problem of wax removal by enveloping a completed and dried shell in a vapor degreaser. The vapor permeated the shell to dissolve and melt the wax. Some measure of success was also found using flash firing methods. Hitchiner developed a wax elimination tank containing hot liquefied reclaimed wax into which a shell would slowly lowered. The wax would melt out due to the transfer of heat to the solidified pattern material. The advent of the steam autoclave for dewaxing shells made these earlier techniques obsolete. In the autoclave, highly pressurized steam rapidly melts the surface of the wax patterns before the bulk of the wax is heated and can expand.

One of the recent major advances in casting technology occurred at Hitchiner Manufacturing Co. when, in the early seventies, the first of its exclusive countergravity casting processes was patented.

Over 4,000 years ago, between the Tigrus and Euphrates Rivers in a land known as Mesopotamia, ancient artisans produced idols and ornaments using natural beeswax for patterns, clay for molds and manually operated bellows for stoking furnaces. Today, precision components for spacecraft and jet engines are investment cast using the latest advances in computer technology, robotics and countergravity casting techniques. The future of the investment casting process is very bright, in part due to the research and development commitment of Hitchiner Manufacturing Co., Inc., the General Motors Corporation and their joint venture company, Metal Casting Technology, Inc.

INVESTMENT CASTING: | Why? | Basics | Tolerances | History | Return to the Hitchiner Home Page. Last modified and validated 1-April-1998.
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The basic technique of investment casting, under its traditional name of lost wax(or cire perdue), has been know for well over six millennia. The precise origin of the proces is unknown. Table 1 shows the estimaded ages of lost wax objects, plotted according to the area where they were manufactured or recovered.
Archeological investigations have indicated Mesopotamia, around 3000-4000 BC, as the location of a civilised society of city states possessing skills in engineering and metallurgy, including the knowledge and the means to produce a range of gold, silver and copper artefacts made by lost wax casting.
Table 1: Estimated ages of lost wax objects.
Another candidate location for the original use of the technique is Thailand/South East Asia, where it is believed that metalurgical activities were carried out by local tribes rather than by urban populations. There is evicence that elaborate bronze artefacts were made by the lost wax method as early as 4500BC in South East Asia.

The Chinese were using the technique from 2000BC onwards and the Egyptians from around 1400BC. An archeological excavation in 1972 of a first century BC Iron Age factory, was particulary interesting, since it provided one of the few examples where clay-based investment moulds wee recovered. Over 7000 fragment were found, for leaded bronze harnesses and chariot fittings.

It is thus clear that knowledge of the investment casting process was widely dipersed in the ancient world, and by the time of Christ appears to have been know and practised in China, South East Asia, Mesopotamia, Egypt, Greece, Italy and Northern Europe, and possibly elsewhere as well.

During the next 1000 years there are isolated references to the process. One remarkable example, dating from 11th century AD or earlier, is Shiva, the Lord of the Dance, 96cm high bronze figure surrounded by a circle representing the cycle of creation, destruction and birth. This investment casting was produced by the Chola dynasty in India, and emphasies their cult of the god-king; the statue is unsurpassed in technical skaill and delicacy of design.

Well before Columbus set sail, the Aztecs in Mexico and the aboriginal Quimbaya goldsmiths in the Cauca Valley, Colombia, were familiar with the process, producing remarkable hollow gold castings.
At about the same time (the 13th century AD) investment casting was the chosen production method for a number of bronze tomb effigies for kings and queens; examples of these are the effigies of king Henry III and Queen Eleanor in Westminster Abbey.
It may be noted that the 14th and 15th centuries represented the flowering of lost wax bronze casting in mid western Nigeria, particularly in Benin, the capital of the Bini region of the country. Probably introduced into the area from the nearby Ife region some centuries before, the techniques became very sophisticated, but were restricted in use to artefacts for the royal household.

Early castings were produced from a wide range of patterns. Archaeological finds indicate that production of identical wax patterns was achieved by the use of dies of carvable stone, cast bronze and carved wood. It is possible that the bronze dies were also used to cast lead by the gravity die process.
The Quimbaya workers probably mass produced patterns for ornamental castings by pressing sheet wax on to the carved surface of stone matrices. In regions as far apart as Africa, India, and South and Central America, it was traditional to build elaborate patterns from wax thread and wire; the wires were wound round a clay or clay/charcoal core, either to cover it wholly or as an open network.
West Afrikaanse Strijder
West African Warrior, bronze,
approximately 1800 AD
Lost wax casting reached possibly its highest artistic expression in Renaissance Italy. Benvenuto Cellini produced many masterpieces by the process, one of the most outstanding being a bronze statue of Perseus holding the head of Medusa. Cellini has left a detailed description of the process, both in treatise of 1568 and in his autobiografie, claiming to have learnt about the casting method
from a descrition by the monk Theophilus Presbyter. Other written evidence of investment casting has come down from about the same time, when Varrinee Krickes of Prague describes the use of the lost wax method to produce bronze gun barrels. In 1538, Vannocio Biringuccio, head of the Papal foundry and a contemporary of Leonardo da Vinci, wrote in his Pirotechnia:

There are likewise moulds for large statues wich, if one desires to make them of bronze, are first made of wax according to the ordinary procedure.
This procedure involved creating an original model or sculpture in wax, wich was subsequently polished and embellished by its creator. Each item was a unique work of art; the image was then coated with a milky slurry of plaster, building up successive layers until a strong shell completely eveloped the wax. After melting out the residual wax, molten metal was pored into the void, wich after removal of the plaster shell left a perfect duplicate of the original pattern form, complete even to undercuts and folds.

Around the 1900s the use of the process was extended to the manufacture of gold fillings and dental inlays for false teeth, and in 1932 the lost wax ceramic block mould process was developed with cobalt-chromium alloys known as "Vitallium", for dental applications and orthopadic components.
Illustrated

CAPTION FOR PICTUREBRONZEAXE
A large variety of gravegoods has been found, especially in barrows of an Early Bronze Age date. Amongst the richest were barrows in the immediate area surrounding large monuments such as Stonehenge. finds include pottery, gold and bronze work, beads, exotic stone, faience, bone, and many other types of materials. a small selection of artefacts found in Wessex barrows is illustrated below.

Bronze objects such as these were produced by the lost wax method of casting and then finished by hammering. the axehead and dagger pictured here came from the Ridgeway barrow in Dorset. They belong to the Wessex 1 phase and date from the period 2000-1800 BC. Awls are another common bronze find.