Pennsylvania holds the second largest collection of post office art in the country -- only New York has more. Artists who competed for commissions from Franklin D. Roosevelt's New Deal programs painted murals that still hang over postmasters' doors today.

On visits to 43 post offices over six years, historian David Lembeck and photographer Michael Mutmansky used large-format photography to document these murals, wood carvings and sculptures that celebrate the state's lush valleys, once-mighty industries and the dignity of rugged citizens laboring in fields, mines, steel mills and rail yards.

The effort is showcased in "A Common Canvas: Pennsylvania's New Deal Post Office Murals." The free exhibition, which runs through May 17 at the State Museum in Harrisburg, highlights what is probably Pennsylvania's largest collection of public art.

Nationwide, the U.S. Treasury Department's Section of Painting and Sculpture commissioned about 1,400 art works during this era, said Francis V. O'Connor, a pre-eminent art historian in New York.

Out of 94 artworks commissioned in Pennsylvania between 1934 and 1943, 88 were created for post offices; five for courthouses in Pittsburgh, Philadelphia and Erie, and one for the U.S. Customs House in Philadelphia. In Pennsylvania, 69 men and 18 women won commissions. Today, 81 of the artworks can still be seen; the others are missing or have been destroyed.

Urged to capture the "American scene," artists created images of sweating farmers, coal miners, steelworkers, glass blowers, railroad employees, hardy pioneers and lumberjacks as well as historic events.

The program dispatched sophisticated artists, often trained in New York or Europe, into small Pennsylvania towns, where they learned what local residents valued.

Those conversations often influenced the art. Residents of Freeland in Luzerne County, for example, insisted that Bucks County impressionist John Fulton Folinsbee paint the local brewery, which sat between two churches.

The commissions provided much-needed work for artists, whose preliminary sketches were approved, then funded by U.S. Treasury administrators. Artists at the time reported being paid $20 to $30 or more per week for their work, roughly $250 to $350 a week in 2009 dollars.

Even 76 years later, "Most of the people notice the art and appreciate it," Mr. Lembeck said.

As he and the photographer worked to collect the images, curious people stopped to tell their own stories. On a hot July day in Irwin, while they photographed a wood relief carving that shows men working with melted steel, a woman in her 70s recalled that even in summer her father wore two flannel shirts to protect his arms from molten metal in the mill.

"That really brought it home to us. All of a sudden, 60 or 70 years ago didn't seem that far away and how dangerous work was, not that long ago," Mr. Lembeck recalled.

Sometimes, the murals ignited controversy.

A 1936 mural for Jeannette's post office portrayed the Battle of Bushy Run of 1763. In his mural, Robert Lepper, a member of the art faculty at Carnegie Institute of Technology (now Carnegie Mellon University), showed British Royal Highlanders using repeating rifles instead of muskets with bayonets.

Jeannette's Postmaster Dillington Shaffer objected, saying repeating rifles did not exist in 1763. He noted that British troops carried muskets they did not have time to reload and won the battle largely because they used bayonets mounted at the ends of their weapons to impale Native Americans.

Bowing to community pressure, section administrator Edward Rowan ordered Mr. Lepper to paint muskets with bayonets in the mural and the artist complied.

In another case, Mr. Rowan proved sympathetic and helpful to a well-intentioned artist caught in a rumor-fueled controversy.

When New York artist Alexander Kostellow painted "Spring Planting," for the post office in Somerset, Somerset County, he could never have imagined that the bucolic scene of a farmer behind a team of two white horses with a red barn and the courthouse in the distance would anger locals.

But Somerset residents already disliked the new and modern, blocky courthouse, which clashed with the town's ornate, neoclassical buildings. The local newspaper blamed U.S. Rep. J. Buell Snyder of Perryopolis, Fayette County, for the new building, calling it an "abomination."

Outrage increased when rumors circulated among local Republicans that the face of the farmer in the mural was actually a portrait of Mr. Snyder, a prominent Democrat. Republicans disliked the congressman because he was an ardent New Dealer who they believed was emptying the U.S. Treasury. Townspeople threatened to boycott the post office and set up an alternative system of delivering mail if the mural was installed.

Dismayed, Mr. Kostellow appealed to Mr. Rowan for help. The administrator sent Mr. Kostellow a backdated letter saying the U.S. Treasury prohibited artists from painting the likenesses of living politicians. Mr. Kostellow showed the letter, dated before work on the mural began, to Somerset residents and the controversy abated.

The free exhibit of "A Common Canvas: Pennsylvania's New Deal Post Office Murals" is displayed at The State Museum of Pennsylvania, 300 N. Street, Harrisburg. 717-787-4980; www.statemuseumpa.org.

Hours are 9 a.m. to 5 p.m. Tuesday through Saturday and noon to 5 p.m. Sunday. It's closed Monday.