Munich Museum Copies Cave Paintings Modern chemical technology, color photography help reproduce Stone Age art at Deutsche Museum Time flipped back some 30,000 years last Friday in Munich, Germany, as the Deutsche Museum unveiled a fullscale replica of the roof of a cave at Altamira, Spain, complete with a copy of its famous Stone Age mural. The original painting—a mineral color rendition of bison, horses, and other animals—is an early and unusual example of man's use of chemical technology. The replica, which took eight years to copy from initial planning to completion, is the featured exhibit of the museum's new department of the origins of chemical technology. The department opened its doors for the first time with the completion of the reproduction. Smaller exhibits show other examples of early chemical technology, including man's use of ocher, fire, and poisons and his work with ceramics and skins. The idea for the new department goes back about a decade, when Dr. R. Sachtleben, head of the department of chemistry of "the museum, conceived the idea of bringing together a group of exhibits showing milestones of early chemical technology. To get the ball rolling, the museum turned to Dr. Erich Pietsch, director of the Gmelin Institute in the Max Planck-Gesellschaft in Frankfurt. Dr. Pietsch was a natural choice for the job. He has long been interested in the history of chemistry, especially in the origins of chemical technology. High-Water Mark. After studying 19 caves in France and Spain, Dr. Pietsch and his wife, Dr. Gisela Pietsch (who has a doctorate in geography), suggested a copy of the Gran Sala of the cave at Altamira. Altamira was discovered in 1879. But the true significance of the painting, which was first considered a fraud, wasn't realized until after the turn of the century. Now it is generally regarded as one of the high-water marks of Stone Age culture. The painting is one of the earliest examples of man's use of multiple mineral colors. In creating their painting, the Stone Age artists used manga-
LOW CEILING. Dr. Erich Pietsch, director of Gmelin Institute, bends head to inspect unpainted roof mural
nese oxide and in some cases carbon for black. And they used various iron oxides to give a spectrum of color from yellow through red to violet. Actually there are several layers of painting believed to span about 15,000 years from about 30,000 to about 15,000 B.C. The mural thus shows how Stone Age art evolved—from simple line drawings to single color work and finally to multicolored work. The museum agreed with Dr. Pietsch and work started. But making a full-scale copy of the roof proved no small task. To get the job done, Dr. Pietsch marshaled the resources of a number of organizations and firms, which freely donated time, money, materials, and manpower as a gift to the museum. They include the
Dyckerhoff Concrete Works, Wiesbaden; the Institute fur Angewandte Geodasie (Institute of Applied Geodosy), Frankfurt/Main; Agfa Film Co., Leverkusen; Wacker-Chemie G.m.b.H., M u n i c h ; Farbwerke Hoechst, A.G., Frankfurt/MainHoechst; Badische Anilin- & SodaFabrik, A.G., Ludwigshafen; Farbenfabriken Bayer, A.G., Leverkusen; Osram G.m.b.H., Munich; and the staff of the Deutsche Museum. To this list must be added Gunther Voglsamer, painter of the Deutsche Museum, who painted the copy, and Dr. Gisela Pietsch, who, with her husband, took the color negatives used in the course of the work. Big Job. From the beginning the job was formidable. When the Spanish government approved the project, it stipulated that the roof must not be touched. The portion of the roof copied is sizable—about 46 square meters. And its physical shape and condition and the dimensions of the cave itself posed problems. For example, the roof is not flat but has waves with amplitudes as great as about 30 centimeters. Also, water has washed away some of the limestone in spots. Furthermore, the distance from floor to ceiling is only about 6 to 7 feet. Thus, it wasn't possible to photograph the roof and reproduce it in any simple way. Special techniques had to be worked out. The first step was to take stereo photographs. With the aid of the Institute of Applied Geodosy, Dr. Pietsch and his team developed a modified form of aerial photography. From 29 accurately located points on the ground, they took overlapping stereo pairs of black and white photographs. Color shots were made at each point, also, but not in stereo. A contour map of the roof was then made, using the stereo pictures. A mapmaking machine called a planigraph was used to analyze each stereo pair and locate points of like elevation. This work took about 1500 hours of machine time. In the third step, the two dimensions of the contour map were converted to a three-dimensional full-scale model made of gypsum. A grinding machine indexed to the contour map ground out a rough approximation of the actual surface on gypsum blocks. The gypsum, hard and brittle, could not be further sculptured directly. So Dr. Pietsch and a team of four helpers added a 3-mm. layer of Plasticine and SEPT.
17, 1962 C&EN
Eight years' work went into the reproduction of the Altamira cave paintings
MAPMAKER. Institute of Applied Geodesy's planigraph was used to analyze stereo pairs and produce contour map STEREO PICS. Twenty-nine stereo black and white photographs were taken from specific points on the cave floor
AERIAL MAP. These pictures are a composite of 29 black and white photos. Portion of mural between heavy lines (above) is what was actually copied. Picture below is, in effect, an aerial map
PEELING. Rolling the finished silicone rubber skin from the working positive had to be done slowly and carefully to avoid damage
GRINDER. Machine, indexed to contour map, grinds out rough approximation of roof on Vi-square-meter gypsum block
HANG ON. Workmen take precarious positions to make "corrections" on map contour after check with cave original
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into this plastic surface worked the fine surface details by hand. They stood the blocks on end, projected a color photo of the corresponding portion of the roof, and molded the surface to match the picture. Details were picked up from enlarged photos. The sculpturing team worked every day for 18 months on this step. The result was a finished positive very close to the real thing. But to make it even more accurate, the team photographed the completed working positive, returned to the cave, and checked it for accuracy. This took 12 10-hour days plus another six weeks back in Munich making corrections. The result was a working positive as accurate as modern technology could make it. Making a Mold. The next job was to make a working negative or mold so that the final copy could be cast. After experimenting with various materials, the group decided to make a mold with a working surface of silicone rubber backed with gypsum for rigidity. In this step, they poured about 800 pounds of liquid silicone rubber (a gift of one week's production from Wacker Chemie) over the working positive, which was protected by a very thin resin film. To make the 46-square-meter silicone rubber skin thus formed more rigid, they added two layers of textile. The final result was a one-piece silicone rubber blanket, 3 to 4 centimeters thick, having all the surface details of the roof in negative. Then to give the skin rigidity, a layer of gypsum in 122 X 2.5 meter sections was cast over the silicone rubber blanket, which still covered the positive. The mold was now complete. Turned over, it could be used to cast the final copy. The 12 backup sections were then lifted off and the silicone rubber skin was rolled up. The next job was to cast the roof in place in the exhibit room. The mold was set up at an angle matching that of the real roof. Dyckerhoff Concrete Works analyzed a limestone sample from Altamira and prepared a closely matching synthetic material— a powder of limestone and silicon dioxide between concrete and limestone. The actual casting was slow and ticklish business. The synthetic material had to be poured slowly and carefully worked into the mold to eliminate all air bubbles. And to slow down hardening and prevent stress cracking, the casting was kept wet for two weeks.
The last job was painting. The idea was to match the Stone Age painting as closely as possible, even in technique. There are several theories as to how Stone Age men applied their colors. One idea is that the colors were applied in blood or fat medium. Such solutions are known to have been used at the end of the Stone Age in open air rock shelters in eastern Spain, Dr. Pietsch says. But Altamira and other caves in France and Spain are closed and wet. A blood or fat solution is hydrophobic, hence wouldn't stick to the wet walls, he adds. Dr. Pietsch thinks that the roof was painted as a "natural fresco" and that the colors were applied using dry sticks or pencils of mineral on the wet wall, or using water solutions of powdered mineral. The film coating the cave walls con-* tains calcium bicarbonate. This film, Dr. Pietsch says, reacts with oxides of manganese and iron to give a mixture of calcium ferrites and ferrates and calcium manganites and manganates which fix the colors as mineralized. Copying the Stone Age. Working with pencils of pure iron and manganese oxides, Mr. Voglsamer and two assistants have spent the past nine months painting the mural in much the same way as their Stone Age counterparts. Not satisfied to copy the roof, Dr. Pietsch, with the aid of Osram G.m.b.H., has also tried to simulate the lighting in the cave as he thinks it was originally. Open fires were not used, since there are no smudge marks on the roof. He thinks that stone lamps fueled with fat were the lighting source. To match this low-level light, Osram will change the resistance of its lamp filaments to give lower temperature light with a higher proportion of red light. As part of his original arrangements with the Spanish government, Dr Pietsch will supervise the making of one more copy in Madrid, using the silicone rubber skin again. The two copies are of more than academic interest. Around the turn of the century, local citizens, unaware of the historic value of the cave, dynamited some of the protruding limestone. This cracked the roof and upset the water balance. This, in turn, has caused some parts of the roof to dry up and flake off and other parts to become so wet that the colors are dissolving. Thus the real painting may one day be completely ruined.