What is Lost-Wax Casting?

Lost-wax casting (also called "investment casting", "precision casting", or cire perdue which has been adopted into English from the French) is the process by which a duplicate metal sculpture (often silver, gold, brass or bronze) is cast from an original sculpture. Intricate works can be achieved by this method.

The oldest known example of this technique is a 6,000-year old amulet from Indus Valley Civilization. Other examples from somewhat later periods are from Mesopotamia in the third millennium B.C. and the objects discovered in the Cave of the Treasure (Nahal Mishmar) hoard in southern Israel, and which belong to the Chalcolithic period (4500–3500 BC). Conservative estimates of age from carbon-14 dating date the items to c. 3700 BC, making them more than 5,700 years old. Lost-wax casting was widespread in Europe until the 18th century, when a piece-moulding process came to predominate.

The steps used in casting small bronze sculptures are fairly standardized, though the process today varies from foundry to foundry. (In modern industrial use, the process is called investment casting.) Variations of the process include: "lost mould", which recognizes that materials other than wax can be used (such as: tallow, resin, tar, and textile); and "waste wax process" (or "waste mould casting"), because the mould is destroyed to remove the cast item.

Process
Casts can be made of the wax model itself, the direct method, or of a wax copy of a model that need not be of wax, the indirect method. These are the steps for the indirect process (the direct method starts at step 7):

1. Model-making. An artist or mould-maker creates an original model from wax, clay, or another material. Wax and oil-based clay are often preferred because these materials retain their softness.
2. Mouldmaking. A mould is made of the original model or sculpture. The rigid outer moulds contain the softer inner mould, which is the exact negative of the original model. Inner moulds are usually made of latex, polyurethane rubber or silicone, which is supported by the outer mould. The outer mould can be made from plaster, but can also be made of fiberglass or other materials. Most moulds are made of at least two pieces, and a shim with keys is placed between the parts during construction so that the mould can be put back together accurately. If there are long, thin pieces extending out of the model, they are often cut off of the original and moulded separately. Sometimes many moulds are needed to recreate the original model, especially for large models.
3. Wax. Once the mould is finished, molten wax is poured into it and swished around until an even coating, usually about 3 mm (​1⁄8 inch) thick, covers the inner surface of the mould. This is repeated until the desired thickness is reached. Another method is to fill the entire mould with molten wax and let it cool until a desired thickness has set on the surface of the mould. After this the rest of the wax is poured out again, the mould is turned upside down and the wax layer is left to cool and harden. With this method it is more difficult to control the overall thickness of the wax layer.
4. Removal of wax. This hollow wax copy of the original model is removed from the mould. The model-maker may reuse the mould to make multiple copies, limited only by the durability of the mould.
5. Chasing. Each hollow wax copy is then "chased": a heated metal tool is used to rub out the marks that show the parting line or flashing where the pieces of the mould came together. The wax is dressed to hide any imperfections. The wax now looks like the finished piece. Wax pieces that were moulded separately can now be heated and attached; foundries often use registration marks to indicate exactly where they go.
6. Spruing. The wax copy is sprued with a treelike structure of wax that will eventually provide paths for the molten casting material to flow and for air to escape. The carefully planned spruing usually begins at the top with a wax "cup," which is attached by wax cylinders to various points on the wax copy. The spruing does not have to be hollow, as it will be melted out later in the process.
7. Slurry. A sprued wax copy is dipped into a slurry of silica, then into a sand-like stucco, or dry crystalline silica of a controlled grain size. The slurry and grit combination is called ceramic shell mould material, although it is not literally made of ceramic. This shell is allowed to dry, and the process is repeated until at least a half-inch coating covers the entire piece. The bigger the piece, the thicker the shell needs to be. Only the inside of the cup is not coated, and the cup's flat top serves as the base upon which the piece stands during this process. The core is also filled with fire-proof material.
8. Burnout. The ceramic shell-coated piece is placed cup-down in a kiln, whose heat hardens the silica coatings into a shell, and the wax melts and runs out. The melted wax can be recovered and reused, although it is often simply burned up. Now all that remains of the original artwork is the negative space formerly occupied by the wax, inside the hardened ceramic shell. The feeder, vent tubes and cup are also now hollow.
9. Testing. The ceramic shell is allowed to cool, then is tested to see if water will flow freely through the feeder and vent tubes. Cracks or leaks can be patched with thick refractory paste. To test the thickness, holes can be drilled into the shell, then patched.
10. Pouring. The shell is reheated in the kiln to harden the patches and remove all traces of moisture, then placed cup-upwards into a tub filled with sand. Metal is melted in a crucible in a furnace, then poured carefully into the shell. The shell has to be hot because otherwise the temperature difference would shatter it. The filled shells are then allowed to cool.
11. Release. The shell is hammered or sand-blasted away, releasing the rough casting. The sprues, which are also faithfully recreated in metal, are cut off, the material to be reused in another casting.
12. Metal-chasing. Just as the wax copies were chased, the casting is worked until the telltale signs of the casting process are removed, so that the casting now looks like the original model. Pits left by air bubbles in the casting and the stubs of the spruing are filed down and polished.

Care & Cleaning of Bronze Statuary & Fountains

Through a variety of finishing processes, bronze statuary is
typically produced with French Brown and Verdigris patinas.

Natural Weathering
Bronze sculptures with a French Brown finish will naturally oxidize to a Verdi Green patina over several years if left outdoors. Bronze Sculptures with a Verdi Green finish will oxidize to a deep green patina. Oxidizing occurs with Bronze Statuary due to its high copper content. Since bronze is an alloy, it contains mostly copper, along with small amounts of tin and zinc. To keep your sculpture clean and if you prefer to maintain the original finish, it is necessary to properly and regularly wax and polish your piece.

Care for Statuary Finishes
Always use a brown wax to maintain your French Brown finish and a clear wax to preserve your Verdi Green finish. We recommend Kiwi Wax as a highly reliable brand. Available from American Custom Wax: 252-955-0156

Applying Wax
Polishing your bronze with a high-quality wax will protect it from nature’s elements. Polishing removes oxidation build-up and dirt spots from your bronze and seals the sculpture from reacting to moisture.

Use a paint brush to apply wax to your bronze sculpture. Start with a light coat over the entire piece, adding additional wax to areas with high detail. Allow the wax to sit for a few minutes, then buff and polish with a rag or electric buffer. If any oxidation or dirt spots remain, repeat the process once more.

Wax should be applied several times yearly for best results, and more often in climates with extreme temperatures or high humidity levels.

Fountains should be winterized in very cold climates. Ensure that both the water pipes and fountain have no residual water and are completely dry and wrapped before the onset of freezing temperatures.

Bronze Statuary & Fountain Securing Guide

Your Bronze Statuary and Fountains may be anchored to the ground to prevent undesired movement or theft. Below are some common examples for mounting a bronze sculpture or fountain to its permanent location.

Bolting
Although many sculpture designs are mounted on a base to provide stability, the base is not designed to prevent accidental tipping. We recommend bolting your piece to a secure base (e.g., a concrete patch, pad or prefabricated metal or wooden base) that can secure the sculpture base. Use a high-torque drill to create holes large enough to fit 3/8” or larger bolts, or use bolting mounting brackets on the base, which can then be secured. A color-matched patina can be used to match the bolts to the base color.

Cementing
Set the sculpture base directly into a curing cement base and allow cement to dry, permanently securing the piece. Note that it will be difficult to move your sculpture from a cement base.

Welding
If other securing options prove untenable, brackets can be welded directly to the base. Use this method only if other options will not produce the desired result. Note that welding results in re-heating the metal sculpture, and it can peel off the finish for up to 12 inches surrounding the weld area, requiring the patina to be color matched and reapplied to the welded area.

Once the bronze sculpture is secured, decorative rocks, stones or landscaping can be added to hide any mounting brackets and water pump equipment.

Shipping

To most of the USA we offer free shipping, there are a very few areas within the US that is very expensive to ship to an example would be into New Your City or some remote locations. If you would happen to live in one of these areas we would give you a call before your credit card is charged and let you know it there would be any extra expense then you can let us know if you would like to proceed with the order or not. 

Free Freight Service:
Most of our items ship by freight truck, the free shipping is considered curb side service with a lift gate, the freight company will give you a call ahead of time when your order is in your area to setup a deliver time with you.

White Glove Freight Service:
We offer a white glove service, where the shipping company will un-package/un-crate your order and set it it where you would like and take the packaging away. Very useful for larger items you might want to order. For a white glove quote please call 866-372-7902 us or email us.

Most of our items are created for a safe delivery, when the item is delivered it is important to check it over before you sign for it. If there is any damage just refuse the shipment and we will send out another order to you. If you are not able to open your shipment for inspection, please make sure you note any damage to the packaging on the receiver sheet (before you sign) no matter how minor (marks, scrapes, gouges ect...) the damage might be to the packaging. That way if you find damage later we can file a claim with the freight company while we send another order out to you. If you don't make any inspections and don't make any notations and you find damage later you will need to file a claim with the freight company.

Damage items must be reported within 72 hours to Unique Mosaic Tables 866-372-7902, if a shipment is refused because of damage please let us know as soon as possible so we can prepare another shipment for you.

If a shipment is returned to us because the freight company can't contact you or you just refused it because you changed your mind, once we receive the shipment back we will inspect it and return a portion of your purchase price to you except for the shipping cost to you and returned shipping cost to back to us.

We can take an order for you and hold it at our warehouse for no extra charge until you are ready for it, but if a delivery is shipped out and you are not ready for it and didn't let us know that you were not wanting it shipped yet, you will be responsible for any storage fees that the freight company might charge for holding your order.