Margot Datz was looking for a pattern but all she found was mossy green. Carefully stripping away small sections of paint at the Old Whaling Church in Edgartown, the muralist was looking for guidance for her next design.

“I was really hoping that we’d find something to tell us which way to go,” she said. But no such luck. “It’s wild to see what the church used to be. Why would they paint it green? Don’t ask me. Maybe there was a paint sale at Edgartown Hardware.”

Martino brothers documented historic restoration in a short film. — Mark Lovewell

And so begins the second phase of the large mural restoration project at the Old Whaling Church. With the back wall of the historic Edgartown church completed in April, Ms. Datz is moving on to the second phase. The two sidewalls and back choir loft will be completed by the annual town meeting in April.

The trompe l’oeil style, or trick on the eye, will continue throughout the Greek Revival church.

With its commanding columns and large window bays, the Whaling Church has stood at the entrance to downtown Edgartown since 1843. The original mural was painted by Carl Wendt in the 1840s, who worked alongside architect Frederic Baylies on the building of many churches around New England. But the mural faded over the past 170 years and last year the Martha’s Vineyard Preservation Trust, which owns the building, moved forward with plans to restore the mural.

The original mural was done in egg tempera. Ms. Datz uses latex paint and oils. Just like she did during phase one, Ms. Datz will have help from her brother Stephen Datz and her daughter Scarlet Blair.

Like the first phase, the initial work is all about the research and design. Ms. Datz is still considering the different possibilities of what the walls may have looked like, based on the other Wendt and Baylies churches in Provincetown and Nantucket. Those have recessed panels, much like the ones Ms. Datz already painted for the back wall.

Ms. Datz said painting the side walls will hold different challenges than the back wall, but that this next phase of design and execution does not call for the “puzzle solving” required for the first phase.

Final unveiling of Whaling Church mural is planned for April 8. — Mark Lovewell

“I think what’s calming about this next phase is if there were any learning curves that we would have to go through — for example palette or application technique — we already nailed it,” she said. “Now it’s very fastidious paint of miles of parallel lines.”

Ms. Datz worked from a historical photograph for the image for the back wall, now it’s up to intelligent design, she said.

“It’s like forensics mixed with intelligent comparison,” she said. “We’re doing the best we can with the existing examples of period painting from that time.”

The second phase comes on the heels of a new short film about the mural restoration project. Martha’s Vineyard Productions documented the entire first phase of restoration project from start to end. The film was created by brothers Dan and Greg Martino.

The eight minute film includes interviews with Ms. Datz and executive director of the Martha’s Vineyard Preservation Trust, Chris Scott.

“We thought it was one of those historic moments in Island history that should be documented,” Dan Martino said. “We like to contribute to the Island’s history and document how the Island is moving, how it’s changing.”

Greg Martino said they hoped the video would be a resource to residents and visitors.

First phase of restoration focused on back wall. Second phase directed at side walls and choir loft. — Mark Lovewell

“People want to come here and see this,” Greg said. “How many people are going to get married under this or visit it? That’s why it’s so important to document it. There is this lack of understanding of history in these buildings on the Island.”

“If you go to Italy or France and see their churches . . . this is our Notre Dame and Coliseum,” Dan added. “It’s one of the most historical buildings in New England.”

Standing in the church with Ms. Datz, the pair said they planned to document the second phase of the project, too. Mr. Scott joined them as the scaffolding went up around the church.

“The big moment is already done, but the neat thing about this phase is the architectural elements,” Mr. Scott said. “Obviously the treatment was intended for the entire church.”

The success of the first phase of the project led an anonymous donor to pledge a $25,000 matching grant at the trust’s annual Taste of the Vineyard Fundraiser. Within minutes, the second phase was funded.

Mr. Scott said he was confident with the design when Ms. Datz first set off to complete the mural. But what he didn’t anticipate was the public reaction.

“The first public viewing was town meeting and the first thing [moderator] Jeff Norton said was, ‘how about Margot Datz,’ and everyone erupted with applause,” he said. “This building is so special to people. It’s such an important building to the town and all the groups that use it.”

The Edgartown annual town meeting, and the final mural’s first public unveiling, is April 8.