Learn how pollution from industrialization in Europe damaged the limestone of Cologne Cathedral

NARRATOR: It took more than 600 years to build this grand cathedral in Cologne, Germany. Ironically, just as the last stones of the cathedral were set into place, Europe was becoming more industrialized and beginning to add significant amounts of polluting contaminants to the air. These contaminants now cause the acid rain that is slowly destroying the stonework of the cathedral. Acids in the rain attack calcium carbonate, the primary constituent of limestone and marble.

These stone carvers and craftsmen are replacing damaged sections of the building. The work combines chemistry, modern engineering, and medieval artistry to re-create the Gothic facades and sculptures that adorn the cathedral. Eroded pieces are replaced with new stones that have a much lower limestone content and therefore will better resist the corrosive effects of acid precipitation.

On scaffolding high up the cathedral walls, the new stones are set into place in the old way, using molten lead to seal the joints. Replacing individual stones and conserving these old treasures has been a costly by-product of our industrial air pollution.