Paul Ray Effinger
Master Sculptor • Jewelry Design • CAD Design • Fine Arts Foundry
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Effinger's Sculpting & Lost Wax Foundry Casting Process

The lost-wax process is a highly skilled art and dates back millennia to the ancient peoples of Persia, Egypt, China and Greece. It basically uses a heat-resistant mold formed around a wax sculpture which is baked to remove the wax, then replaced by molten metal poured into the same mold.

The modern ceramic shell lost-wax process is difficult and labor intensive and why it's expensive. Much detail must be paid to the many steps in reproducing a sculpture in metal, often requiring months of labor to arrive at the final castings. And every step must function perfectly! The sculpture is basically created three times in different media: the original clay or 3D model, the wax copy, and the bronze copy.

At right are my sons Luke and Paul performing foundry work 2012.

Paul & Luke Effinger

8-11-14 Casting

The process is very accurate, and will reproduce a thumbprint in the wax. Although the ancient process is generally the same as that used today, significant modern advances include:

  • hi-tech ceramic cement used to make the investment mold (or ceramic shell)
  • standardized: waxes (e.g. victory wax), metal alloys (e.g. silicon bronze) and chemical patinas
  • polyurethane and silicon rubber molds (to generate wax-positives)
  • Computer Aided Design (CAD), Computer Aided Manufacturing (CAM) & Computer Aided Visualization & Animation
  • CNC Milling, TIG welders and plasma cutters
  • hi-resolution 3D printers

The Sculpture

I use traditional art skills, mechanical engineering, digital technology and live models to create my sculptures. Sometimes I sculpt the model in clay, but I prefer creating them digitally and 3D printing when possible. Sculpting and designing digitally can save months of time when creating a sculpture. I can do things digitally that take forever to do by hand in clay. Precision is much higher digitally since you can zoom in as much as desired to add detail. The drawbacks are the high print costs and the long learning curves to master the software.

Generally, I don't wish to create an exact likeness of the model, but rather use their natural beauty to serve as an anatomical foundation for what I'm designing or creating.

Below, is the CAD model of Volnus I designed using Max and ZBrush modeling software.

Volnus wip Volnus Sectioned

3D Printing

Hi-resolution 3D Printing and CAD modeling have changed the face of modern manufacture.

I was introduced to 3D printers while taking my first engineering class at UT Austin in 1984 and have kept apprised of them since. However, only in the past few years have they had high enough resolution and been economically feasible to use for my sculpture.

At right are hi-resolution prints I created for my 18" high, limited bronze edition of Volnus.

The model was printed for 90 hours on an Objet Eden 500V printer with a vertical Z-axis resolution of 16 microns.

The material is an ABS plastic, hard but brittle, but easy to work with.

I sanded the Volnus model later (after this photo was taken) with automotive sandpaper, alternating with coats of sandable gray primer, producing a very smooth model, that I molded in rubber (see next section).

Volnus

The Rubber-Mold

In order to reproduce an artwork in bronze, it must first exist in wax form. This usually means creating rubber-molds of the artwork and often dividing it into several pieces (as shown above) to cast it properly. Making molds is generally the most time consuming and costly step of the foundry process and an art in itself. Well-made molds are critical to the success of good bronze castings. Careful study determines the best way to divide the artwork for molding.

Precision molding often involves vaccuuming the rubber prior to use to reduce bubble defects on the mold's surface. The rubber is then brushed, sprayed, or poured onto the sculpture, then backed by a rigid "mother-mold" of plaster, fiberglass, or wooden frame which holds the rubber in place after the sculpture has been removed, and subsequently when wax is poured into the mold to make the wax-positive. Often the soft clay original is destroyed as it's removed from the rubber-mold, so sometimes you only get one chance to make it right.

Below is the complex rubbermold I made for Volnus. The mold for the body part was created by pouring liquid rubber around the gray model suspended in a box, cured overnight, and then separated from the model. The pieces fit back together like a jigsaw puzzle. Generally molds only have two or three pieces. New technologies are now possible to print the rubber mold directly, bypassing the need for even creating a physical model.

Mold Preperation Body Wax

The Wax-Positive

Wax-positives reproduce accurately in bronze during casting, even a fingerprint will transfer, but the wax shrinks about 10% compared to the original. There's also another shrinkage of 5% from wax to bronze.

To cast bronze properly it generally needs to be cast as a hollow shell. This beneficially minimizes weight and expense. As bronze solidifies, it contracts and "pulls" away from areas still molten. Smaller or thin masses (i.e. the sculpture masses) need to solidify before larger masses (i.e. heat sinks such as the funnel and main sprue).

Hollowing ensures large surface areas of the sculpture dissipate heat quickly and solidify first. A hollow wax-positive is made for larger pieces by pouring hot liquid wax into the rubber-mold, sloshing it around to coat the inner walls of the mold where it condenses, then poured out. This is repeated a number of times until a shell of wax is formed on the inside of the rubber-mold. The thickness of the wax shell represents the final bronze thickness. When the wax cools, the mold is opened and the wax-positive is removed.

Waxes of various hardness, melting point, and color are used for different purposes, sometimes mixed together.

Volnus Wing

Below are the final hollow wax positives for Volnus' body and wings prior to spruing. All imperfections (e.g. pinholes, bubbles, cracks, etc.) have been fixed.

bodywax back
bodywax front

Below the body and legs have had sections removed to facilitate the ceramic slurry for the investment (see below); these plates will be welded back on after casting.

a b
c

Below are the hollowed wings. They'll be cut into three pieces each to ensure good casting.

wing wax-positives

If a part is relatively small, it can be cast solid as the 4" left-leg piece shown at right.

Depending on the size/complexity of the piece, other parts of the sculpture can be attached in the wax phase or cast separately and welded together later. I find it's usually better to seperate the pieces if possible, since casting smaller pieces is easier, but you have to keep in mind where the TIG torch-head has clearance to get into. Keep the cuts in the middle of limbs or the middle of the torso, so there's good working room from all angles when welding, chasing and polishing the seams.

As a final step of the wax phase, the artist signs their name and records the Artist's Proof No. (AP #) or Limited Edition No. (LE #) on the wax sculpture. AP's are created first, reserved for the artist and close friends, and usually valued more than the LE's. AP's usually have unique differences compared to the LE's.

Volnus Wax Leg

Shown at right are all the wax positives John Kasson made for my sculpture Evening Mood in 2005.

The Kassons created molds down to the smallest strands of hair! I'm very fortunate to have learned from second-generation founder, John Kasson.

Eve waxes

Spruing

Sprues are the wax tubes that direct molten bronze to the sculpture from the funnel, and vents are the tubes that allow gases to escape and route back to the outside top of the funnel.

Wax-positives and sprue-systems are thoughtfully and carefully designed to provide molten bronze to the sculpture as it solidifies; if they're not, the casting may be voided of metal as it cools and ruined. It doesn't matter if the heat sinks void or distort, as they're cut off later. The funnel also pools impurities which rise to the top of the molten bronze.

A funnel (made by filling a cup with wax) is attached to the top of the sprue-system, and directs the bronze as it's poured into the ceramic mold.

A steel hook/pipe is placed in the wax cup to facilitate dipping into the ceramic slurry and hanging during drying. Square or rectangular main sprues attach below the cup to inhibit vortices and turbulence of the bronze (which is undesirable) as it enters the cavities of the ceramic mold; they're often tapered at the bottom before attaching to the sculpture to act as a choke point, so air is not sucked in with the bronze, but also to increase pressure to make sure bronze is forced through all the secondary sprues. Secondary sprues are reverse tilted, which fill as the bronze rises, and ensure backflow to main sculpture surfaces.

The bronze flow makes a cylindric path, kind of like blood in our bodies - it travels from the heart or funnel, downward through the center, through all the extremeties, and back up again towards the top of the funnel.

sprued wings

Ceramic Shell Investment

The wax sprue-tree is sealed with shellac spray or dipped in a degreaser (pattern wash) prior to investment, so the slurry adheres to it well. The tree is then dipped in a large vat of ceramic slurry and immediately coated with refractory stucco (fused silica) and allowed to dry. The slurry is made of microscopic colloidal-silica-binder mixed with refractory-flour, wetting-agent, and anti-foam.

1 2 3

This is repeated 8-20 times as necessary over several days to build a ceramic shell mold thick enough to withstand the forces of molten bronze required for the casting.

The first coats are coated with a fine stucco to capture detail, followed by a course stucco to build thickness.

The shell becomes heavier, thicker, and stronger with each successive dip. Large investments require reinforcement using wire, dowels or fiberglass after the fourth coat, to support the heavier masses of molten bronze.

A hook or pipe embedded through the top of the wax funnel aids in handling the heavy investment and for hanging it as it dries. It falls out during burnout.

Basically, each foundry has its own unique procedures, techniques and recipes to create the shell, to accomodate different castings, but they're still similar.

The white ceramic shell encases the wax positive and allowed to dry fully overnight, before burnout can begin.

Investments

Burnout

Kiln Burnout 2014

The ceramic shells are then placed in a flash kiln at 1500 F where the wax and water are thoroughly burned out or "lost" in a matter of minutes, and they solidify and strengthen.

Shown here is my dewaxing kiln and a shell baking inside. The wax runs out holes connected to pipes in the bottom and is collected and recycled.

Larger foundries will first place the shells in an autoclave (pressure cooker) to remove the wax before burnout. This eliminates the stress and possible cracks due to expansion of the wax as it's fired in the kiln.

The burned ceramic shells become lightweight (through lost wax and water), have very fine surface detail, can withstand extreme thermal shock, are very porous, dissipate heat quickly, brittle but quite strong, and easily devested from the bronze castings.

After burnout, the investments are cooled, inspected, and any cracks are patched with a mixture of slurry, stucco and sometimes fiberglass cloth for reinforcement, and fired again prior to the pour.

It's common to develop cracks in shells dewaxed in a kiln due to extreme pressures of the wax inside the shells, but holes can be drilled at stress points in the shells to relieve the pressure and avoid cracks. Holes and cracks are easily repaired and patched later and hardened on preheat before the bronze pour. I get better results putting the shell in the freezer 1-2 hours before burnout, which contracts the wax and causes less cracking than drilling holes.

Bronze Casting

I use pure Everdur 873 Alpha silicon bronze ingots (95% copper, 4% silicon, 1% manganese) with a solidus of 1590F and a liquidus of 1790F.

The solidus is the temperature at which the metal is completely frozen and the liquidus is the temperature at which the metal becomes liquid; in between is a mushy state due to the various melting points of the alloys. Unlike pure metals, alloys solidify over a range of temperatures. Pouring temperature is in the range of 1900F to 2100F depending on the mass and shape of the sculpture.

It takes roughly an hour to melt the bronze depending on the amount charged. The crucible is placed into the gas-fired furnace and charged with the proper amount of bronze. Once the furnace is ignited, air/fuel mixture is adjusted to an oxidizing atmosphere and the furnace roars as the bronze is heated.

The ceramic shells are placed in the kiln and pre-heated to avoid thermal shock and thus cracking while receiving molten bronze.

Slag is removed from the top of the liquid bronze (where it collects) using a steel skimmer. Temperature is measured with a digital tungsten pyrometer immersed into the metal.

Once the target temperature of the bronze is reached, ~ 2000 F, then the magic happens quickly. The kiln and furnace are shut off and the glowing hot investments are removed from the kiln with kevlar gloves and supported in a bed of sand.

Pour 9-2012

The glowing hot crucible radiates unbelievable heat and protective clothing is required. It's lifted from the furnace by two foundrymen and placed onto a firebrick on the floor, inside a pouring/lifting shank.

They then lift the shank, which grabs the crucible below its bulge, lock it in place with a lever, and hoist it above the lip of the ceramic investments where the molten bronze is carefully poured in, slowly enough to allow gases to escape.

Sometimes, several investments are filled with a single charge, or the crucible may be recharged for more pouring. After pouring, any excess bronze is poured into ingot molds for later reuse, and the crucible scraped out, and cooled.

Luke and Paul
Luke and I pouring 7-14-14 at night.
Casting Done
8-11-14 Early morning pour in the heat of Texas summer. The shells below have just been filled with bronze and now cooling.

Devestment

As the casting cools about half an hour, the ceramic shell begins to crack and is easily devested from the bronze by tapping/chipping with a hammer or pnuematic hammer. When thoroughly cooled, all ceramic is removed, bronze sprues are cut off, and pieces are separated. The bronze scrap is recycled. The ceramic shell provides an extremely fine surface on the bronze.

Volnus devestment Wing Devestment

There's so much that can go wrong, but when it goes right it's awesome. The body casting on Volnus was complex but came out superb.

Volnus Body Casting

Chasing & Welding

Surface defects are chased, welded, cleaned, polished, and multiple cast pieces are TIG welded together. This can take hours, days, or weeks, depending on the size and complexity of the sculpture, and how much effort is needed to smooth the surface.

Below, the body sprues have been chased or cut off using various metal grinders and cutting wheels.

sprues removed

Below, I'm welding the back plate onto the body. Each piece is welded on, chased and polished, until the entire sculpture is assembled.

Paul welding body
backplate welded

Each wing was cast in three pieces and welded together, as shown below. The bluing is caused by the heat of the torch which is easily removed later during a final sandblasting which cleans the surface prior to patinization.

TIG Welding Wing

Polishing

Below is some of the initial polishing on the body using rouge and a high-speed buffing wheel. Bronze shines so beautiful, but oxidizes so quickly.

body polishing

Below the wings have been welded on and chased.

wings welded on

Patinization

Patinization is the application of chemicals that react with the bronze to achieve color.

This is a highly skilled art, with many different techniques, such as hot, cold, or fumed patinas - often involving a multitude of toxic recipes. Sculptures displayed indoors and outdoors generally require different patinas.

The patina can make or break a sculpture, and is about as important as the subject matter itself.

I was planning to patina Volnus, but after the initial polishing, I liked it so much as is, I decided to just lacquer and wax the bronze to seal it.

 

Patinas

Sealing

The finished sculpture is sometimes sealed with lacquer and almost always waxed to provide a beautiful protective barrier that should last for years to come. The polished bronze has just been laquered in the photo below.

lacquered

Mounting

A base of fine wood, marble or granite is usually chosen to display the sculpture. The base is often drilled with holes and countersunk to allow screws to fasten the bronze to it and the bronze is also drilled and tapped to receive the screws. Sometimes the sculpture is set on bearings for fully rotateable viewing.

Below, I fastened my finished bronze sculpture to a fine black granite base using two 1/4" bolts I tapped into the buttocks.

Volnus Polished Finish

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