Bronze - Ancient And Modern Alloy

 Bronze is an alloy that goes back at least to the 4th millennium B.C. Bronze artifacts have been found in what is now known as Iran and Iraq. It was one of the most innovative and important alloys ever created by humans. It is much harder than pure copper or stone, and for this reason bronze was used to make many different kind of tools, weapons, other kinds of implements, armor, decorative tiles and statues.

Bronze was used to make cannons because it causes very little friction in metal to metal applications. Iron cannon balls could be used in a bronze cannon without any fear of the ball sticking in the barrel. The relatively low melting point of the alloy and its malleability made it the most used type of metal for centuries. So many things were made from it that a period of human history is known as The Bronze Age.

The two main metals that comprise bronze are copper and tin. As these two metals are not commonly found in the same areas, historians think that when the alloy became more widely known and in demand, that this led to increased trade in the ancient world. Most bronze is 88 percent copper and 12 percent tin. Bronze is still used to make many items today. As it does not generate sparks when struck against a hard surface, it is used to make mallets, hammers, wrenches and other tools used in high explosive areas and areas with flammable vapors. It is also used for springs and all types of bearings, especially bearings for use in small electric motors.

One of the most common uses of the alloy in ancient and modern times is the casting of statues. Highly detailed molds can be used because bronze has some unique characteristics. It expands slightly before it completely sets, thus filling all the finely detailed areas of a mold. Bronze also shrinks slightly when it is completely set, thus making it very easy to remove from molds.

The progression of human learning has created many new things to replace the old. While bronze is not so extensively used as it was in ancient times, there is no modern replacement for it. It is still the best material for certain uses. It is truly an ancient and modern alloy.

Lost Wax Casting of Bronze

The traditional process used to cast bronze, developed and used 4,000 years ago, is called lost wax casting. This method results in highly detailed, quality castings and has changed very little over the centuries. The method was used by craftsmen and artists from every culture from ancient Mesopotamia and Egypt up to today. 

 This process begins with the object that is to be cast. An artist creates a sculpture from clay or wax as these substances remain soft. These sculptures can be very intricate and finely detailed. A mold is then made of the sculpture, usually in two pieces, sometimes more when a sculpture is very large. Plaster is used on small pieces, but fiberglass is also used, especially for larger sculptures. After the molding material has been applied and it has dried thoroughly, the mold is then opened and the original sculpture is removed. Usually the original is destroyed in this process, as the molding material is very rigid. That is why the original sculpture is made of a soft material so that it can be removed from the mold.

After all of the original sculpture has been removed and the mold cleaned, a thin coating of wax is brushed onto the inside of the mold. This is done to capture every intricate detail of the mold. The mold is then put together, and wax is poured in the mold while it is being slowly rotated. After a layer of wax at least three quarters of an inch forms on the inside of the mold, the rest of the wax is dumped out. When the wax has thoroughly hardened, the mold is removed. The wax cast is then worked on by artisans to ensure that it is as perfect as possible. The wax casts are then dipped into a mixture of plaster and sand. This is repeated many times. Each dipping has to dry thoroughly before the next. With each successive dip, the sand and plaster mixture gets more coarse. This results in a very strong shell being built up over the wax cast. After these shells have hardened, vents and 'runners' are added to allow the molten bronze to enter the shell, and for gases and excess metal to escape. 

The shells are then placed into a kiln and baked at very high temperatures. This heat causes the wax inside of the shell to melt away, leaving an exact image of the sculpture in the shell. This gives the process its name of 'lost wax casting'. After baking, the shell is now a mold ready for molten bronze. Once the bronze has been poured and has cooled, the shell is then carefully chipped away, leaving a cast of the original sculpture in bronze. Any flaws are removed, the sculpture can be buffed and left its natural bronze color, or painted. This process is very labor intensive and expensive, but it results in such fine quality castings that it is still used after 4000 years.