Spyra wondered if the sole surviving painting of an eruption reflected reality or was a painterly exaggeration. By comparing the size of the volcano in the painting to the size of the real thing, which rises nearly 56 feet above the river that flows past, he could then tell that the smoke in the painting represented a cloud 30 feet high. That, he says, meant the smoke could have been from a natural source—and that the painting was a good guide to what the original "eruption" looked like.
But what kind of wood would they have used? Why was the volcano so far removed from the rest of the prince’s property? Why were there three separate fireplaces concealed in a brick-lined chamber under the volcano’s peak?
Ironically, the most important clues came from a contemporary critic named Carl August Boettinger, who wrote a lengthy eyewitness report in 1797 ridiculing the spectacle of a volcano plunked down in the middle of the eccentric prince's estate. While making fun of Franz, Boettinger described the "eruption" in detail—from the water released from the concealed "crater" at the top of the volcano to simulate lava to the red lamps that gave the pile of stone an otherworldly glow.
With that to go on, "we started out by researching what the people of the time might have used for fireworks," Spyra says. Gunpowder, pitch and sulfur were readily available to 18th-century pyrotechnicians, most of whom were military men intimately familiar with explosives. Bengal fire—a bright blue or red flame not unlike today's road flares—was also well-known.
As re-created by Spyra, the event is impressive, even to 21st-century eyes accustomed to special effects and fireworks. As the twilight deepened into what German poets call the "blue hour," that moment just before the sky goes black, a deep hush settled over the crowd.
Then, with a final rumble of drums and thunder, the moment arrives: red flames flickered at the top of the volcano, growing into a thick column of smoke.
Red-tinged water begins to flow from the crater, churning the still lake below. Sharp, loud explosions send sparks shooting into the sky. Hidden in the volcano's peak is an 86-square-foot oven packed with fresh pine needles. Once lit, they roar into smoky fire, sending sparks high into the night sky along with the billowing smoke.
As the needles burn above their heads, Brandenburg Technical University students in gas masks rush from fireplace to fireplace in the room below, squirting lighter fluid on blazing wood fires and tossing in special powder to create brightly colored smoke that pours out from underneath the summit of the volcano.
Then, red-tinged water begins to flow from the crater, churning the still lake below. To create the illusion of flowing lava, Spyra first filled the artificial pond at the top of the crater. As the volcanic "eruption" peaks, the water is released over a ledge to form a waterfall, lit from behind by bright red Bengal fire.
Throughout, sharp, loud explosions send sparks shooting into the sky, jolting onlookers with each loud bang. The effect is produced using mortars, familiar to any 18th-century artillery expert.