The scenario of all its phases.
"How to make a bronze sculpture?"

Bruce Krebs, sculptor, explains the different stages of the art foundry from one of his pieces.

versions :
The original is laid flat.
Here, the original is made of plaster. But it can be made in any other materials.

The sequence of these phases is explained from a piece existing of
Bruce Krebs, installed on the ramparts of La Rochelle This bas relief is called "From generation to generation".
The silicone elastomer is poured over the plaster
The silicone elastomer perfectly takes the impression of the part.
Would you like to see the original in plaster just before the Elastomer casting?

It’s a cover of support.
Over the silicone elastomer a plaster or resin screed is created to hold the elastomer with fixed markers.
Without this screed the mould, too supple, could not return exactly the copy of the original piece.
We turn the set.
The original plaster piece is removed from the mould.
It’s a delicate moment because the original plaster can break.

It’s quite funny to watch because the characters are hollow...
The wax
Before pouring the liquid wax into the elastomeric imprint, The bottom of the mould is brushed with wax at a good temperature to ensure that all the details of the mould are obtained.
Then liquid wax is poured into the elastomeric imprint. The wax, at the right temperature, enters the mould. We need to get the overfilled before the wax hardens, to maintain a constant wax thickness.
The flow system.
We’re building a network of wax rods. (it is necessary to imagine that the wax, once evaporated, will become the network that will lead the bronze to fusion. This liquid bronze must innervate" the whole piece without forgetting a part to allow the proper distribution of the molten metal in all parts of the piece. )
The refractory plaster
The wax and its ventings are coated with refractory plaster. This plaster is the beginning of the second mould.
Removal of elastomer mould.
We turn the whole thing over, and remove the elastomeric mould delicately so as not to damage the wax. The wax then discovers its main face.

During this action, we must be very careful not to tear the Elasto. This mould will be ready for another order...
Alteration of the sculptor.
After this succession of operations, the sculptor rediscovers his sculpture in wax. He alone can know what is of his hand and what is an incident of journey. It’s up to him to correct it.
The installation of the ventings.
Ventings are small wax stems. They are stuck above the fronts of the characters, on the middle of the books. They are connected by large vertical rods. This network, during the casting of the bronze in fusion, later, will allow to evacuate the air.

On the photo, the white stems have another function: they will be used to maintain the thickness of the piece. Indeed, with the pressure of the molten bronze , the bas-relief could thicken, the plaster alone would not resist...

So there are two separate systems: the bronze distribution system and the air exhaust system.
Second layer of refractory plaster.
The front face is also coated with refractory plaster.

The assembly is then reinforced with a solid reinforcement, a sort of "bodice" to prevent the part from bursting under the influence of heat.

In the picture, we can distinguish (in green) the output of the supply network "the casting path", and all ventings outlets (in light yellow). This tank is then filled with refractory plaster.
The furnace
The unit is placed in a furnace.
The lost wax
After a stay in the high-temperature oven that lasts an entire night, the wax melts. But unlike the candle that flows as it melts, This one "evaporates". By disappearing, the wax leaves a void of air inside the refractory plaster. The wax network has become a hollow network. "The wax is lost !" That’s the name that they call this type of mold.
The casting of bronze in fusion
Remember, there are two separate networks.
The largest distributes bronze in fusion. Through this channel called "casting path" the bonze is immediately transported to the bottom of the mould. Once he’s down, it goes up into the mold, chasing the air upwards. The second network allows the air to escape when the bronze rises in the piece. It is at this moment that we better understand the usefulness of the network of wax rods prepared previously...

This moment is dangerous. If any water particles are present in the mold, the melting "explodes"... The mold may break under pressure and the bronze will spread...
Bronze cools very quickly.
It is therefore necessary to be sharp and precise at the time of this operation because the bronze must not solidify until it has invaded all parts of the mould...
Break the refractory plaster mould.
Every smelter has his own method. It is only then that we discover whether the bronze casting is really successful. If a problem has arisen, the elastomeric mould must be taken back and new wax poured into it... (See above)
Give me a good shower, please!
In the photo, the white parts are not snow sheets in spring! but a remnant of the refractory plaster. Everything must disappear.

We also discover the entire network of ventings, which is also now made of bronze...
the chiselure
It is now necessary to cut the vents with the stoning,and chisel the bronze, correct, if necessary, remove all small cooking defects.
This work is very long because it must be very thorough..
- If a bubble has occurred during casting, it becomes a bubble in the metal, it must be sealed with a weld.

Here is a short film of 1 minute 30 seconds "the chiselure" that I realized about another sculpture entitled: "The curiosity"
- If there was a small bubble in the Elastomer, it becomes a growth that needs to be suppressed...

- If a micro-crack occurred in the refractory plaster during casting, this crack can create a very fine growth that must be eliminated, of course.

The sculptor intervenes to verify that the chisel is in conformity with what he created. He’s the only one who knows it.
Last gesture of the founder: the patina.
The patina is an acceleration of the aging of the bronze by the addition of different chemicals (Especially nitrates) and heavy torch reheating.

Or if you want, it’s the initiation of an aging of the piece, for whatever you do, a bronze never ends with skating, It’s a natural metal process to get old.

C'est le sculpteur qui décide de la couleur et de sa densité. Le patineur tente de reproduire ces choix...
No patina looks like another, even if they are made on the same day by the same founder...

The founder is also an artist (or not). Also, the sculptor must place complete confidence in the talent of his founder.

Here is a short film of 1 minute 30 seconds "the patina" that I realized about another sculpture entitled: "The Masters of the World".


Do you want to know

Do you want to know

the history of this part ?

the work of Bruce Krebs ?

Bruce Krebs, sculptor
9 ter rue Amelot, 17 000 La Rochelle, France, Europe.
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