Frankfurt, the secret capital city

© HMF, Petra Welzel

Enormous snow globe showcases the many faces of a city

Museums are always looking for new and unusual presentation methods. The Historische Museum Frankfurt (Historical Museum Frankfurt) is displaying various models of the city under an enormous PLEXIGLAS® dome.

The giant PLEXIGLAS® snow globe in the Historische Museum Frankfurt is not only used to showcase the exhibits, but is also a truly spectacular exhibit in its own right. Raised up from the cellar by an industrial robot, the models depict eight different perspectives of the city of Frankfurt. Not only is it fascinating and interesting – it is also an unusual way to present exhibits.

Visitors can select each of the eight models at the touch of a button. “Visitors really like this way of presenting exhibits and try to get as close to the PLEXIGLAS® dome as they can. The concept provides them with a full view of the robot working in the illuminated room one level below the snow globe,” says the museum’s Director Dr. Jan Gerchow. “It is just like a giant jukebox.”

Get a first-hand look of the snow globe at the Historische Museum Frankfurt. / Source: YouTube/inSynergie GmbH

Snow globe meets multimedia presentation

Instead of simply depicting the history of the city of Frankfurt, the models created by international artists show the city’s different facets. Frankfurt is painted as a financial center, as the crime capital, or as a city characterized by numerous construction sites. While the model makes its way upwards into the globe, accompanying animations are projected on the snow globe, which is as tall as an adult man. “The installation is truly spectacular, however, it is more a poetic than overwhelming exhibit. It gives visitors the time and space to really think about the scenes created by the artists,” says Dr. Gerchow.

Dr. Gerchow is convinced that “the snow globe is the most exceptional exhibit in the entire museum. I think all visitors will take their time exploring it.” He also adds that it is unlikely that all visitors will see all eight models. All in all, it takes six minutes to switch the models. It takes three minutes for the robot to move the models up and down, and each model then rotates in the snow globe and is illuminated for three minutes.

Facts and figures on the PLEXIGLAS® snow globe

A 320-kilogram block of PLEXIGLAS® GS was used to create the snow globe. The completed globe has a diameter of 2.4 meters, is 1.6 meters tall (excluding the base) and three centimeters thick, and has a net weight of 210 kilograms. Its transparent, colorless, smooth and seamless design ensures that visitors at the Historische Museum Frankfurt have an unobstructed view of the exhibits inside the globe. The globe was manufactured by the PLEXIGLAS® experts at Birkholz Kunststoffwerk GmbH from Heppenheim.

Perfect view of the exhibits

The snow globe was manufactured from Evonik’s brand acrylic glass PLEXIGLAS®. Why? “The material boasts outstanding optical properties. It was imperative that the material of the globe was colorless and was not tinted, while regular polishing should not affect the surface. This meant that PLEXIGLAS® was the ideal choice for us. PLEXIGLAS® is highly transparent and offers an unobstructed view of the models inside the globe, even given its curved shape,” explains Thomas Schmitt, Managing Director at Birkholz Kunststoffwerk GmbH. The company was commissioned to manufacture the snow globe by inSynergie GmbH, the general contractor for installation. “There simply is no other material with these outstanding optical properties – much less at this size.”

A bigger PLEXIGLAS® sheet was needed

The path to the finished installation was marked by many obstacles, however, and the production of the giant snow globe proved to be quite challenging. Schmitt and his colleagues had to break new ground in the process. “We are quite familiar with forming sheets made of transparent plastics, but we never had to shape sheets of this size,” say Schmitt. The three-centimeter-thick PLEXIGLAS® GS sheets are usually two meters wide and three meters long, but that was not enough to manufacture the snow globe. Evonik therefore supplied a block which was six-by-three meters, a size that is usually used to create breathtaking large aquariums and spectacular swimming pools. This size was sufficient to produce both a sample as well as the final snow globe.

There simply is no other material with these outstanding optical properties – much less at this size.

Thomas Schmitt
Managing Director at Birkholz Kunststoffwerk GmbH

Failed first attempt

In the first step, the plastic experts at Birkholz heat the PLEXIGLAS® for two hours in an oven at 180°C. They first had to modify the oven, as it was originally designed for a material width of 2.7 meters. The heated acrylic glass was then stretched over a hollow mold made of foamed material, and then formed to a globe by sucking it into the mold using vacuum pumps. But the result was a little discouraging, as the globe was not thick enough at the top.

The fourth time was the charm

The hollow mold was revised and the oven and tensioning frame were modified. Schmitt and his team tinkered with and modified the parameters and they even had to order a second PLEXIGLAS® block. In the fourth attempt, they succeeded in producing a globe with the desired properties. “The entire team was very relieved. Manufacturing a semi-sphere would have been no problem whatsoever, but rather than ending at the center, the snow globe goes all the way down to the base. This was a tremendous challenge for us, as we had never tried anything like this before,” says Schmitt.

After cooling, the employees removed the globe from the hollow mold. But it would be wrong to think that this already marked the end of a successful project. “Two colleagues spent two weeks grinding and polishing the entire globe surface in an elaborate manual process, until it sparkled like a diamond,” recalls Schmitt.

Transported into the museum by crane

The globe’s 60 kilometer journey from Heppenheim in southern Hesse to Frankfurt went very smoothly. Using a crane, the 210-kg snow globe was lifted into the basement of the museum through an opening in the floor. “It was a fantastic feeling to witness our globe being fitted onto the base. We were just really happy and proud to see that all our plans finally came to fruition,” says Schmitt.

See for yourself how the snow globe was lifted into the museum and how it works. / Source: YouTube/inSynergie GmbH

We have had only good experiences with PLEXIGLAS® in the past.

Dr. Jan Gerchow
Direktor Historisches Museum Frankfurt

Since the museum reopened in October 2017, the snow globe still shines as new and attracts a lot of visitors. “We are highly satisfied with the result. We have had only good experiences with PLEXIGLAS® in the past. The round shape in particular meant that extremely high requirements were placed on the material,” says Dr. Gerchow in retrospect. “The snow globe is truly extraordinary. And it is something that all generations enjoy.”