Creating a hollow cast bronze sculpture brings together the artist’s vision and the traditional skills of the foundry. By using the lost wax bronze casting process, a carefully created wax model is transformed into a rough cast bronze replica, before being refined and finished by hand
The work involves much more than pouring molten metal. Research, modelling, mould making, casting, chasing and patination, each stage contributes to the character and quality of the finished sculpture, and its cost reflects far more than the value of the bronze metal it is created from
The stages below follow the traditional workshop approach, from subject research to the final patina. Foundry methods, mould construction, casting temperatures and wall thickness vary with the sculpture and casting methods, so the dimensions and temperatures given, are examples rather than universal specifications
From the artist’s creativity in sculpting the original model and producing the wax replica, to the specialist knowledge required to cast the bronze successfully and the skilled craftsmanship needed to apply the final patina, each stage demands experience, precision and time
Because much of the process is done by hand, each bronze is unique and no two castings are ever completely identical, even when produced from the same original mould. These subtle variations are a hallmark of authentic bronze sculpture, reflecting the artistry and craftsmanship invested in every piece
Creating a realistic and finely detailed bronze sculpture begins long before the first piece of clay or wax is shaped. It starts with careful research and a collection of reference material, ensuring the artist fully understands the subject from every possible angle
Particular attention is given to photographs that capture the expression, character and personality, that the artist and commissioner wish to preserve in the finished sculpture. It is often these subtle details that transform a good likeness into a truly memorable portrait
By carefully studying and selecting the most appropriate reference images, the artist can create a sculpture that is both life-like and meaningful, faithfully capturing not only the subject’s appearance but also their individual character
Where appropriate, we use modern digital technologies to improve the accuracy of portrait commissions, while ensuring the traditional hand-crafted lost wax casting process remains unchanged
With the research complete, the artist begins creating the original model. Depending on the project and the preferred working method, this may be sculpted in modelling wax, clay or other oil-based materials that remain soft and workable throughout the creative process
At Escar UK Bronze we generally favour modelling wax because of its exceptional versatility. Unlike clay, it does not usually require an internal armature (supporting framework), allowing the artist to concentrate on developing the form rather than constructing additional support
By blending different grades of modelling wax and specialist additives, the material can be tailored to suit the needs of each project. Its hardness, flexibility and working characteristics can all be adjusted, giving the artist complete control throughout the sculpting process
One of modelling wax’s greatest advantages is its sensitivity to temperature. When cool it becomes firm enough for carving crisp details into the wax. As it warms, it softens into a pliable material that can be shaped, modelled and refined with ease. It can even be heated until liquid and applied with a brush to build delicate layers, or it can be allowed to cool slightly before being applied with a spatula or sculpting knife, whenever a greater thickness is required
Once cooled, modelling wax is capable of capturing an extraordinary level of fine detail, making it particularly well suited to portraiture and intricate sculptures
Unlike clay, modelling wax does not dry out, allowing work to be paused and resumed, without affecting the model. This is especially valuable for commissioned sculptures where adjustments or client feedback, may be incorporated over an extended period
Another important benefit is that modelling wax can be reused many times. Material removed during sculpting can be remelted and recycled, making it both economical and ideal for refining a design, until the artist is completely satisfied with the result
Finally, modelling wax offers complete flexibility throughout the creative process, allowing material to be added, removed or reshaped with ease, as the sculpture evolves
Once the original wax model has been completed, a two-part mould is created to capture every detail of the sculpture. The mould consists of an inner flexible layer and a rigid outer support shell, which can be disassembled and reassembled with complete accuracy
The inner mould is typically formed by carefully applying successive layers of latex or silicone over the wax model until the required thickness is achieved. This flexible layer faithfully reproduces every texture, contour and fine detail created by the artist, before being left to cure
To protect and support the flexible inner mould, a rigid outer shell commonly made from plaster or fibreglass, is then constructed around it
During this stage, locating flanges incorporating interlocking register pegs are formed around the mould. These ensure the two halves separate cleanly once cured, and more importantly, fit back together in exactly the same position every time they are reassembled
Where necessary, bolt holes are drilled through the flanges to be able to secure the two mould halves firmly together, to prevent even the slightest movement during subsequent stages of the casting process
Once fully cured, the mould is carefully opened and removed from the original wax model, preserving every detail ready for the next stage of production
Over time and after repeated use, even the highest quality moulds will gradually lose some definition. In addition, the flexible silicone components can occasionally suffer minor damage due to their delicate nature
For this reason, mould condition is carefully monitored throughout the production process to ensure every wax positive remains faithful to the original sculpture, in both detail and quality
If any degradation is detected, the existing wax model is returned to the artist for refinement. Where necessary a new mould is then created from the updated model, ensuring the integrity and detail of the edition is fully maintained. The previous mould is then retired
The two halves of the mould are carefully reassembled and secured before molten modelling wax is introduced into the cavity. For smaller sculptures the mould is gently rotated so the liquid wax coats the entire inner surface, creating an even layer to the desired thickness
Every artist develops their own preferred techniques, and uses carefully judged quantities of wax to achieve the ideal wall thickness for each sculpture
For larger sculptures, where rotating the mould is impractical, the wax is usually applied by hand in successive layers until the required thickness, of typically around 3 mm is achieved
Once the wax has cooled and hardened, either naturally, or for smaller moulds by force cooling with water, a hollow wax positive is produced. This is a faithful replica of the original model and will eventually become the bronze sculpture
The flexible mould is then carefully removed from the wax positive. Where multiple castings are required, the mould can be reused repeatedly to produce identical wax positives for each edition
Between castings, the reusable flexible mould can be cleaned, inspected and stored for further authorised wax positives. This is different from the ceramic casting shell, which is broken away after each bronze pour. Reusing a mould does not change the size of subsequent castings
Before the casting process continues, the wax positive is inspected and where necessary, carefully chased to remove any minor imperfections
Chasing is a traditional finishing technique in which heated metal tools are used to smooth the wax surface, refine fine details and eliminate the faint seam line created where the two halves of the mould meet. This ensures the wax positive faithfully reflects the artist’s original work, before progressing to the next stage of the lost wax casting process
For smaller sculptures, the hollow mould containing the cooled wax inner coating is placed upside down in a bed of sand to support it securely, while the internal supporting core is formed
A ceramic slurry is prepared by mixing a specialist refractory powder with water. A proportion of sand is then added to increase its strength before the mixture is poured into the hollow wax positive
Once the slurry has set it is removed from the sand, the outer silicon/ fiberglass mould is removed, and we have a ceramic wax coated solid core which now now forms the inner half of the full mould
For larger sculptures an additional stage known as spruing is carried out before the ceramic outer half of the mould is created
Solid wax rods known as sprues are attached to the outside of the wax positive to form a network of channels. During the casting process these channels serve two essential purposes
When the mould is heated the molten wax drains away through the sprues, leaving a series of hollow passages within the outer ceramic shell. Later when molten bronze is poured into the mould, these same passages allow air and gases to escape, while guiding the bronze into every part of the mould. This helps to ensure a complete and successful casting
Once the wax positive has been sprued, it is coated with successive layers of ceramic slurry and fine refractory sand. This process follows the same principles used for smaller castings but is adapted to accommodate the greater size and complexity of larger sculptures
Where a sculpture is particularly large or has a long narrow form, the mould is separated into two halves. The inner surfaces are coated individually first in wax, then in ceramic, before the sections are reassembled. These become the inner and outer wax filled ceramic moulds
Additional layers of ceramic slurry and refractory sand are applied until a shell approximately 12 mm (½ inch) thick has been built up. The shell is then reinforced with wire and further ceramic layers to provide the strength needed to withstand the casting process
Depending on the design of the sculpture, the ceramic shell may remain as a single assembly or be divided into separate sections. Larger or more complex sculptures are often cast in individual pieces, before being expertly welded together during the finishing stage
Once the ceramic shell has fully hardened metal locating pins are driven through the outer shell, through the wax layer, and into the inner ceramic core. These pins ensure the inner core remains perfectly aligned after the wax has been melted away, maintaining a consistent wall thickness throughout the finished bronze casting
Before the ceramic mould is ready to receive the molten bronze, it is thoroughly inspected to ensure it is structurally sound and free from defects
Any weak areas or minor damage are carefully repaired, while unwanted openings are sealed to prevent leaks during casting. Where necessary, additional openings may also be incorporated to assist with wax removal during the firing process
For larger castings, strategically positioned openings are formed around the base of the mould and temporarily sealed with wax plugs. As the mounds are brought up to temperature, these plugs melt away providing controlled drainage paths for the molten wax
After the wax has drained away the drain holes are plugged with ceramic, to prevent any leakage of molten bronze during the pour
If the firing method is traditional, once the ceramic mould is ready it is carefully positioned and large slow-burning logs are arranged beneath and around it
A temporary kiln is then constructed around the mould and logs, using breeze blocks for the walls and a metal roof above to retain the heat. Once built, kindling is placed between the logs and the kiln walls, the fire is lit, and it is carefully tended as the temperature gradually increases
The logs are left to burn slowly overnight allowing the ceramic mould to heat evenly. This gradual heating is essential, to help to prevent the mould from cracking when the 1,200°C molten bronze is poured in the following day
Eventually the temperature is high enough to melt the wax, the wax drains away and the mould is now left with a hollow void inside ready for the bronze pour. It is this stage that gives the process its name, the Lost Wax Bronze Casting Process
While the ceramic mould is being prepared, bronze ingots are melted in a separate furnace, ready for casting
The furnace is traditionally fuelled with wood, while a forced-air blower supplies additional oxygen to intensify the fire and raise the temperature to approximately 1,200°C. At this temperature, the bronze becomes fully molten and is ready to be carefully poured into the prepared mould
With the ceramic mould fully prepared and the bronze heated to its molten state, the casting process can begin
The molten bronze is carefully transferred from the furnace to the mould in a crucible, before being steadily poured into the prepared openings at the top. As the bronze flows down through the internal channels, it fills every part of the cavity left behind by the lost wax
Once the mould has been completely filled, the bronze is left to cool and solidify under carefully controlled conditions. This gradual cooling helps the casting retain its precise shape, structural integrity and fine surface detail
The bronze pour is one of the most critical stages of the entire process, where careful temperature control, timing and experience, combine to produce a high-quality bronze casting ready for the finishing stages
Once the bronze has cooled sufficiently, the ceramic mould is carefully broken away to reveal the casting within. The outer shell is broken away with hammers and the inner ceramic core is drilled out
The wax sprues, now replaced with bronze metal, are cut off to be melted down and recycled for future castings. The ceramic inner core and outer shell however, have fulfilled their purpose and are destroyed during this stage
The bronze casting has now emerged from the mould, but is still far from being a finished sculpture. Before patination can begin, the casting undergoes an extensive process of cleaning, refining and finishing
Generally, the larger the casting, the more finishing work is required. Any remaining traces of the casting process must be carefully removed before the bronze is ready for its final surface finish
This stage, commonly known as metal chasing or fettling, involves using grinders and other specialist tools, to remove the bronze sprues, eliminate the casting seams and dress the surface, until the sculpture faithfully reflects the artist’s original work
Any imperfections are then corrected. Excess bronze is ground away, small casting defects and/or surface pits are repaired, and areas where the bronze has not cast perfectly, are rebuilt by welding before being carefully re-shaped and blended into the surrounding surface
Where a sculpture has been cast in several sections, these components are expertly welded together and the joints meticulously dressed until they become virtually invisible
Finally, the finest details are restored or enhance using precision grinders and rotary tools, fitted with a variety of specialist burrs. Fur, feathers, hair, skin texture and other intricate features are refined by hand, bringing the sculpture to life before the final patination is applied
With all the finishing work complete, the bronze is ready for the final stage, the application of it’s transforming patination. Carefully selected chemical solutions are applied to the heated bronze, to create specialised colour and tonal effects
Once the desired patina has been achieved, the surface is protected with successive coats of specialist wax. The first coats are applied while the bronze is still warm to ensure deep penetration, followed by additional cold applications. The sculpture is then carefully buffed to produce a rich enduring lustre, while providing long lasting protection for the bronze below
Bronze sculpture manufacturing combines artistic modelling with mould making, casting and hand finishing. Each stage of bronze sculpture production contributes to the final work, from the original design, to the chased surface and chosen finishing patina
Creating a bronze sculpture is a team effort, combining the foundry’s craftsmanship and experience with creative practical problem solving. Every member matters, from those preparing the moulds, casting and finishing the bronze, to the person carefully wrapping the completed sculpture for its journey overseas
We listen to one another, respect each person’s expertise and work together to find solutions when a commission calls for something unusual. The quality of the finished work and its safe arrival at its destination, is the sum of everyone’s contribution
We hope this insight has been informative and has helped illustrate the level of skill, craftsmanship and attention to detail that does into producing a traditional lost wax bronze casting
Every bronze sculpture is therefore far more than a cast metal object. It is the culmination of artistic vision, traditional craftsmanship and countless hours of skilled hand work
Bronze statues and sculptures are commonly made using the lost wax bronze casting process, a form of investment casting. An artist creates a model, then a mould is used to produce a wax replica. The wax is enclosed in a heat resistant mould and melted out, leaving a cavity for molten bronze. Once cooled, the casting is released, cleaned and finished by hand. Larger pieces may be cast in sections and welded together before patination and protective waxing
A genuine hollow cast bronze sculpture has walls of bronze metal around a hollow interior. Usually made by lost wax casting, it uses less metal and weighs less than an equivalent sculpture cast solid throughout. The hollow construction does not make it imitation bronze
Bronze resin, also called cold cast or bonded bronze, combines resin with bronze powder rather than being cast from molten bronze. Both materials can reproduce fine detail, but bronze resin and genuine cast bronze are different materials
The wax replica is melted out of a heat resistant mould before molten bronze is poured into the space it leaves behind. The wax pattern is therefore “lost” during each casting. The bronze reproduces its shape and surface detail
Ceramic shell bronze casting is a form of bronze investment casting. Layers of ceramic slurry and refractory material build a heat resistant shell around the prepared wax pattern. After the wax has been removed and the mould prepared for pouring, molten bronze fills the cavity. A core can define the hollow interior of a sculpture
Wax chasing refines the wax replica before casting, removing mould seams and correcting small surface flaws. Bronze chasing and fettling take place after casting: unwanted metal is removed, welded joints are blended and fine details are restored before the final surface finish
Bronze sculpture patination develops the surface colour through controlled chemical reactions, often using heat. The bronze patina process follows chasing and other finishing work. Protective wax is then applied. Patination is part of the bronze surface treatment rather than an ordinary coat of decorative paint
The flexible master mould can be used to make more wax replicas while it remains in suitable condition. Each wax replica needs its own heat resistant casting mould or ceramic shell, which is normally broken away to release the bronze. Further casts must remain within any agreed edition limits
For a bespoke project, visit our commissioned bronze sculptures page for design, quotation, timescale and installation information
Wikipedia -:- For more information on the 6,500 year old Art of Lost Wax Casting -:- The Crucible
Hollow Cast Bronze Statues UK -:- Hollow Cast Bronze Sculptures UK
Escar UK Bronze