Restorationist Ralph Mills knows the century-old stained-glass windows at Tarentum’s Central Presbyterian Church.

“I’ve been here from the first, in 2014,” he said about 12 large windows that his Pittsburgh-based specialty company cleaned, repaired, preserved and reinstalled. The windows were new when the church opened in 1913.

Two weeks ago, Mills, who is co-owner of Pittsburgh Stained Glass Studios, was working with windows at an older church in Nashville, Tenn.

Mills said the staff is usually working at two churches across the country and has windows and frames for seven or eight other churches disassembled at the studio’s work benches and labs.

Lewis Comfort Tiffany popularized the U.S. pictorial opalescent glass style — with seven or eight layers — starting in the 1880s.

Central Presbyterian’s windows are in Tiffany’s style but were produced by the Highland Art Glass Co. in Pittsburgh. That company used mostly two-layered, lifelike colors and detail.

But 100 years of pollution and everyday street grime started to dull the beauty. And the chemical nature of almost pure lead started to cause chemical reaction problems not understood when the church doors were opened in a bustling Tarentum. Lead mixed with an alloy, called restoration lead, is used now.

A well-intended decision started to get in the way of seeing the images and colors, church manager Dave Rankin said.

In the 1960s, attaching protective plastic sheeting seemed to be right solution to guard against vandalism. But that caused a problem: the plastic sheets yellowed with age and that obscured the bright colors.

The small but active congregation started to raise money in 1999. It also obtained grants from the Pittsburgh History & Landmarks Foundation and the Ira Wood Charitable Trust.

Fifteen years later, the restoration work began.

In the five years since, about a dozen large windows have been repaired and reinstalled in the sanctuary. Last week, the biggest of 40 movable windows — which allows them to swing open of ventilation — were installed at the front of the church.

Meanwhile, the congregation continues to provide breakfast and lunch for at least 20 people. It holds Sunday school and services and hosts a long list of community projects.

The first sanctuary window to be worked on by Stained Glass Studios was about 8 feet wide and 12 feet tall depicting Jesus the Good Shepherd.

Work is under way for the smaller windows.

Still, the work is not complete.

There are two large skylights in the sanctuary, that started to leak in the 1990s. They were capped, again, with plastic.

“We’d like to repair those and bring in more light,” Rankin said.

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