A new mural has gone up on a wall in Center City Philadelphia. Don't blink or you'll miss it.

Dubbed "Freewall," a program of temporary outdoor murals has been launched at 12th and Sansom streets.

Sansom Street, between 12th and 13th, might be one of the noisiest blocks in Philadelphia. Garbage bays, construction crews, and helicopters on the roof of nearby Jefferson Hospital create an urban din. Awkward slashes of sunlight slicing between towering buildings create their own cacophony of shadows.

On a wall overlooking a parking lot next to Fergie's Pub, an abstraction of color and shape swirl across stucco. The lines could have been made by a subtle flick of a wrist, had they been put on a canvas in an artist's studio. But these are on an enormous scale. Some passers-by say it looks like a stampede of horses on fire.

"It's a collection of sensations," said artist Robert Goodman, who tailored the mural specifically for this location. "The sensation of being in this space. Sensations of seeing a mark that appears handmade with a small gesture but knowing it's a big form. Having a sense of being overwhelmed by broad architectural shapes."

The mural, called "The Tumble," is temporary. It is the first of the "Freewall" series, which will be whitewashed in six months to make way for a new mural. The idea was hatched by the owner of Fergie's Pub--Fergie Carey--and artist David Guinn.

Guinn has worked many times with Philadelphia Mural Arts Program and its signature community-based development process. But he wanted the content of "Freewall" to be a personal expression of the artist, not the larger community. That's why it's temporary.

"That was part of the bargain with not having a community process," said Guinn. "If you're going to have something put up permanently, there's a responsibility to make sure everybody's on board. If you're going to put up something temporarily, people can assess, enjoy, criticize, but it isn't something anyone's going to have to live with permanently."

'Spirit of adventure' infuses short-lived work

Impermanence grants the artist freedom a typical mural does not.

"If I had thought this was going to be here forever, I think I would have had less of a spirit of adventure," said Goodman. "Knowing that it would be temporary, there were some freedoms I allowed myself that were important for this project to be successful."

Temporary also means it's cheaper. Artists can use regular house paint instead of tougher, more expensive mural paint. The $2,500 needed to make "Tumble" was raised through Kickstarter (plus an additional $200 for, well, kicks), and Guinn says the next mural, to come in the spring, will require another fundraising effort.

Artists will be chosen through an application process. The next artist to follow Goodman has not yet been determined.

Fergie Carey, of Fergie's Pub, lives in the Bella Vista neighborhood and watched as Guinn's mural "Autumn," at Ninth and Bainbridge, became the centerpiece of a real estate fight between neighbors who loved the mural and a developer whose rowhouse would obscure it. The developer won.

That happened just as the building next to Carey's bar in Center City was torn down to make room for a new development. Carey offered his bar's newly exposed exterior wall to Guinn.

Just as the murals on "Freewall" are temporary, "Freewall" itself may be fleeting. Carey says a new building -- a tower -- is in the early planning stages. Once completed, it will eliminate that exposed wall space.