The Associated Press reports that Trinity Cathedral is being cleaned in preparation for the Episcopal Diocese of Pittsburgh's 250th anniversary, a yearlong celebration that will begin on Thanksgiving.

Crews have begun cleaning the blackened cathedral, built in 1872, with a solution of baking soda and water. Slowly, the tan color of the sandstone has emerged.

The grime from the city's steel and coke mills turns acidic when it rains, and has been eating away at the building’s limestone, according to the AP.
"There had been some debate within the diocese about whether or not to clean it," Bishop Robert Duncan told the Pittsburgh Post-Gazette. Some members of the diocese thought the blackened exterior would serve as a reminder of Pittsburgh's industrious past. But the bishop said he could look out of his office windows and see the deterioration. In 2000, he and some colleagues hired an engineering firm to take a sample of the grime and test it.
The cost of the project won’t be known until the cleaning is done, the newspaper reported. The cleaning is expected to take three to four months.

Landscapers and others are also cleaning headstones in an adjacent cemetery. The graveyard was originally an American Indian burial area but also holds the remains of French and British soldiers from Fort Duquesne and Fort Pitt and early Americans from the city's 18th century origins.

The cathedral is the second church building on the site. Then-rector, the Rev. John Henry Hopkins (who was a lawyer, architect, and priest), designed a Gothic brick structure covered with stucco to look like stone. Bishop William White, the first Bishop of Pennsylvania, consecrated the new Trinity Church in 1825, according to a history of the cathedral.