From Stone Age to High Tech - Wacker Chemie AG

From Stone Age to High Tech

The Lascaux cave, with its 17,000-year-old paintings is a World Heritage Site, but the sheer number of visitors has taken its toll. To preserve the original paintings for future generations, the French company AFSP has produced detailed replicas of the cave walls using ELASTOSIL® M silicone rubber from WACKER.

A view inside the copy of the Lascaux cave: modern reproduction techniques create new ways of exhibiting cultural heritage.

These art works date back around 17,000 years, having survived the end of the last Ice Age, the Bronze Age, and the Greco-Roman era. It was only in the Modern Age - 1940 to be specific - that the Stone Age paintings of Lascaux were rediscovered. The cave complex is situated in southwest France, about 150 kilometers north of Toulouse, in the commune of Montignac. Concealed in the rock are some 2,000 wall paintings, covering several hundred square meters, chiefly showing animals. The skillful rendition of bulls, reindeer and horses soon became known as the “Stone Age Sistine Chapel.”

“ELASTOSIL® allows every detail of the polystyrene master mold to be transferred to the imitation stone panels.”

Hans-Rudolf Pfeffer head of Technical Marketing, Industrial Solutions
Specialists from AFSP correct the final reproduction of a cave panel using a coarse-grained stone paste.

This cultural jewel, which had endured for millennia since prehistoric times,now found itself threatened by hordes of visitors streaming through after the Lascaux cave was opened to the public in 1948. Particularly the moisture exhaled by the many visitors – up to 1,200 per day – affected the highly sensitive cave climate. The delicate biological equilibrium was thrown out of kilter – a veil of algae, mineral deposits and microorganisms began to spread over the wall paintings (see box). Consequently, in 1963 – after only 15 years – the cave complex was closed to visitors again, and an elaborate ventilation system was installed. But pressure remained high to make the Stone Age masterpieces accessible to the public once again.

Detailed Copy

The elastic silicone mold is released from the final reproduction by members of the international AFSP team.

Eventually, the French state opted to have a copy made of the entire cave complex. The detailed replicas with an area of about 900 square meters are housed in a modern exhibition at the foot of the Lascaux hills. At the 6,000-square-meter International Center for Cave Painting in Montignac-Lascaux, visitors can experience all the original cave paintings. Formally opened in December 2016 by President François Hollande, this permanent exhibition is known as Lascaux 4. It is the third replica of the original cave of Lascaux 1, which was closed to the public in 1963. UNESCO has since declared this and other caves in the Vézère valley a World HeritageSite.

Danger from Microorganisms

Before the Lascaux cave was discovered in the 1940s, it had not been exposed to humans for a long time. Such self-contained biotopes are often a paradise for specially adapted microorganisms, which form a sophisticated ecosystem that leaves the paintings undamaged. If conditions change, different microorganisms that can damage the art works reproduce.

As early as 1960 – only twelve years after the cultural monument had been opened to visitors – green algae could be seen on the walls. The delicate equilibrium previously maintained by the system became unbalanced. Only three years later, the conservators saw themselves forced to start combating the green biofilm growing there. They used a number of agents for this, including various antibiotics and chemicals.

At the turn of the millennium, another threat emerged, this time not green but white. Fusarium fungi colonized the cave, covering the walls with a white fuzz. Since, 2006, black patches have also been weaving their way from ceiling to floor. To combat all these fungi, the conservators again resorted to a cocktail of antibiotics and chemicals, together with elaborate physical cleaning and improved ventilation. Another partial victory in the battle to preserve the 17,000-year-old Lascaux Stone Age masterpieces for future generations.

In 1983, the first visitors walked through the facsimile caverns of Lascaux 2, containing some 90 percent of the wall paintings. This mecca for Stone Age enthusiasts has since been viewed by ten million people. ’Such a stream of visitors is bound to cause damage, so, after the three decades that Lascaux 2 had been open, we were involved in the urgent repair work,” explains Francis Ringenbach, artistic director and head of production at the Atelier des Fac-Similés du Perigord – AFSP. The company developed a process for scanning a cave in three dimensions and using the data to produce a millimeter-accurate reproduction from an artificial stone. The choice of silicone for moldmaking was the result of close technical cooperation between Group Gazechim (a WACKER partner in France) and AFSP.

The silicone elastomer is applied to the polystyrene model to produce a negative mold.

For both Lascaux 3, a mobile exhibition on show across the world since 2012, and now Lascaux 4, the AFSP experts have reproduced the cave complex in panels corresponding to the original Lascaux 1. They invoke in visitors the same feelings that stirred the four teenagers, when, on September 12, 1940, they became the first people in thousands of years to walk through the halls of Lascaux and see with their own eyes the unique character of this Stone Age monument.

The Lascaux cave complex is located in South-Western France, 150 kilometers north of Toulouse. Stone Age hunters probably sheltered here during the last Ice Age, the Würm glaciation.

In the process developed by AFSP, the scientists map out the original Lascaux 1 cave with great precision using a 3D scanner, and take photos of all the walls. This data enables them to make accurate copies of the wall contours using 50 polystyrene panels, into which the shapes taken from the 3D scans are cut. On average, they correspond to about 20 square meters of the original wall surface. The conservators apply a molding compound to the foam polystyrene panels by hand to complete a faithful copy of the original: the master mold. They also manually transfer the colored reference points of the wall paintings

From the 3D Scan to the Replica

The deceptively realistic imitation of the Lascaux cave is the result of state-of-the-art computer technology, years of experience with the materials, and a sensitive artistic touch.

  1. Preparing a Master Mold
    Foam polystyrene blocks are cut to size based on the 3D scan. The technicians smooth over unevenness with a mineral coat. They mark the outlines of the paintings with reference points.
  2. Copying the Master Mold
    A layer of ELASTOSIL® M silicone (yellow) is transferred to the master, copying all the details. It is part of the negative mold.
  3. Preparing the Negative Mold
    The negative mold is stabilized with casting resin and a metal scaffold. Then the polystyrene master mold is removed.
  4. The ReplicaIs Created
    The specialists transfer the veil of stone onto the negative mold.
  5. The Negative Mold Is No Longer Needed
    It is supported by another casting resin coat, while stability is provided by a metal scaffold. The stabilizing casting resin coat and the silicone of the negative mold are removed.
  6. Finalizing the Panels
    After the ELASTOSIL® M coat has been removed, experts apply patina to the imitation stone that remains. Finally, they add the original wall paintings using the reference points duplicated in the silicone as a guideline.

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.