The world’s most famous frescoes — what Michelangelo painted on the Sistine Chapel’s ceiling and altar wall — were in the news again this week, as the Catholic Church’s cardinals met there and chose a new pope.

Coincidentally, at the same time, several College of Charleston students also created what may be downtown’s only fresco.

A close-up look at what they did shows why artistic works in this medium are so rare these days.

Architectural history professor Ralph Muldrow painted one in graduate school and got the idea to tackle another while making small talk at a party with art history professor Alvaro Ibarra.

“We had an extra cup of punch,” Muldrow says, “and that might have assisted our decision.”

They chose the same image that Muldrow painted: the Delphic Sibyl, a small part of the Sistine Chapel.

The work began by special ordering lime putty from Virginia (it’s only recently been made commercially in America) and ordering red iron oxide, yellow iron oxide and cobalt blue from Germany.

“The pigment has to be mineral-based because the lime is caustic,” Muldrow says. “If you tried to use an organic color, the lime would eat it up.”

The first few coats had to be applied days apart about a week before the final coat to give them time to cure. “It doesn’t just dry, it actually recomposes itself chemically as a strong version of calcium carbonate,” Muldrow says.

Meanwhile, the students created a paper pattern with the image of the Delphic Sibyl so they could trace its outline on the plaster.

Before the powdered pigments can be mixed with water, they must be ground, or mulled, even finer. “The term ‘to mull things over came’ from that practice,” Muldrow says.

The fine powdered pigment slips into the pores of the lime putty, eventually binding itself to the hardened plaster.

“That’s why they could clean the ceilings in the Sistine Chapel. It’s because the colors, which turned out to be brighter than they thought, were part of the plaster,” he notes.

On painting day, a final coat is applied and the pigment is done as the plaster is still wet.

All of the colors had to be created by mixing the three primary pigment colors.

Catherine Stillwaggon, one of about a half-dozen students who worked on the fresco, says the biggest challenge is trying to keep the pigment moist. They needed about two hours to finish the 2-by-2-foot image.

Muldrow says Michelangelo also took care to do one figure a day, partly because as the image dries, it shrinks.

“He wanted to make the cracking, which would inevitably happen, happen between the figures he did each day,” Muldrow says, “so if it cracked, it would further frame the subjects.”

Fresco work is rare in the United States. Most of the better-known American murals were done with oil paint on canvas, then affixed to walls.

“Essentially, we did just what Michelangelo would have done, except very talented painting,” Muldrow says.

Of course, there’s another reason to be even more impressed with the Renaissance work. It was done atop rickety wooden supports.

The students did their work safely on the ground behind 12 Bull St.

“We asked the dean for a 30-foot scaffold,” Muldrow jokes, “but she said no.”

Award presentation

The College of Charleston will bestow its Caroline & Albert Simons Jr. medal of excellence award Thursday to Alexandria, Va., architect Allan Greenberg.

The event, which includes a lecture by Greenberg, will be at 7 p.m. in Room 309 of the Simons Center for the Arts. It’s free and the public may attend.

Reach Robert Behre at 937-5771.