From Stone Age to High Tech - Wacker Chemie AG

From Stone Age to High Tech

Easy Separation

From a 3D scan, foam polystyrene blocks are cut to size (below), and – via the silicone negative mold – an imitation stone positive mold is then made (top).

Then, to ensure that the positive and negative molds can separate easily, a modern material comes into play: the two-component silicone rubber ELASTOSIL® M from WACKER. “It allows us to transfer every detail of the foam polystyrene master mold, including the mineral molding compound and color to the synthetic stone panels,” explains Hans-Rudolf Pfeffer, who is responsible for technical support for silicone moldmaking compounds. ’Reproduction with ELASTOSIL® M is so accurate that it can even be used to copy a vinyl record,” notes Pfeffer. He actually didn’t believe it until he had tried it himself.

“With our silicone rubber, you can even faithfully copy a vinyl record.”

Hans-Rudolf Pfeffer head of Technical Marketing, Industrial Solutions

ELASTOSIL® M is the ideal material for copying the cave walls, not just because of its fidelity. The silicone can be easily processed and, with the right formulation and curing agent, it vulcanizes rapidly even at room temperature, so it can be processed without expensive equipment. In addition, the material retains its shape: shrinkage on vulcanization either does not occur or is only marginal. “The resulting polymer is robust and durable, and the molds can be used to make hundreds of reproductions,” says Hans-Rudolf Pfeffer. The raised reference points of the wall paintings are transferred to the vulcanized silicone rubber.

The experts took about three months to make each panel.

To allow the silicone layer to serve as a negative mold for the artificial stone, it is stabilized with a layer of resin - the support mold. The two parts are not permanently bonded, so that the high flexibility of the silicone rubber can be utilized for handling.

The AFSP staff support the shell with a metal scaffold and remove the foam polystyrene master. The material the experts finally apply to the silicone layer cures to give the look and feel of a stone wall. This artificial stone is extremely durable and resistant, and is based on a mixture developed and patented by AFSP.

Resin Support Mold

The new state-of-the-art visitor center featuring the replica Lascaux cave is nestled in the hills of southwest France.

Once the technicians have also applied resin to the stone layer and the dried panels have been stabilized with a metal scaffold, they remove the support mold from the resin. At this stage, ELASTOSIL® M remains on the artificial stone. The reference points of the cave paintings from the master mold have now been transferred to the artificial stone. The silicone layer can then be peeled off the copy. In the last step, the artists manually apply patina to the artificial stone and add the reference points to the original cave paintings. 70 international specialists were involved in the project, working, on average, for about three months on each panel. The AFSP team thus contributed to the continued conservation of the Lascaux 1 World Heritage Site, while making the 17,000-year-old masterpiece publicly accessible. Lascaux 4 provides a framework in which the visitor can experience the cultural treasure in a historical context in one of the most modern exhibition galleries in the world – thanks to intricate craftsmanship, the latest 3D computer technology and the multifaceted talents of silicone.