The glass pipes and bongs usually associated with smoking marijuana aren't just for smoking anymore. as one museum exhibit in Old City will posit when it opens Friday, they're art.

Put that in your pipe and smoke it.

The National Liberty Museum launches "The Treachery of Images," a monthlong art exhibit displaying more than 50 glass hand and water pipes (also known as bongs) from about 20 prominent American pipemakers and glass artists. The museum, which is billing the exhibit as the first glass-pipe show in a museum setting, also will offer displayed work for sale. While most pipes in the exhibit are worth thousands of dollars (one, titled "Freija," is valued at $250,000), the focus here will be on freedom.

"We are a museum about freedom and liberty, celebrating freedoms of expression and speech, tolerance and acceptance, and freedom from oppression," says museum glass director Meegan Coll. "These works are true pieces of art, beautiful and descriptive of their place in time, their cultural context, and the surrounding community."

The exhibit's title is a play on a 1929 painting of the same name by Belgian surrealist artist René Magritte. Underlining the image of a pipe with the phrase "Ceci n'est pas une pipe" (or "This is not a pipe"), the painting implores viewers to question their interpretations of reality by pointing out that the painting is not a pipe, but rather an image of a pipe. The exhibit itself will echo that message, asking attendees to see what's displayed not just as pipes, but also works of art, especially amid changing attitudes toward marijuana.

While the exhibit may sound like an odd choice for a mainstream museum, the move is a logical one to Philadelphia pipemaker Marble Slinger, a longtime glassblower operating out of North Philadelphia's Mount Krushmore studio. Slinger, who directed the glass-pipe documentary Degenerate Art, says that pipes are an artistic expression of the ever-growing marijuana-legalization movement and have evolved as art.

"The work has matured to a level where it's worthy of being recognized by higher institutions, on top of the fact that the laws have softened to make it more acceptable socially," said Slinger, whose work will appear in the show. "Having a nice pipe is saying, 'Instead of herb smoking being demonized, I think it should be celebrated.' "

Philadelphia is home to one of the most vibrant glass-pipe-making scenes in the country thanks to artists like Slinger, Josh Opdenaker, Nate Purcell (Just Another Glassblower), Zach Puchowitz, and others who have set up shop here. Many, in fact, are Philadelphia natives or were educated at institutions such as Temple University's Tyler School of Art, the Crefeld School in Chestnut Hill, or Salem Community College in New Jersey.

"We're part of this weird, greater tradition," says Germ, also known as Jeremy Grant-Levine, a Krushmore pipemaker, who also will have work on display at the show. "It's interesting, too, because there are other cities with big scenes, but we're in Pennsylvania. We're probably the only major pipemaking city that's in an illegal state."

That scene, regardless of its state's laws, will be on full display through May 7 alongside nonpipe glasswork from more traditional glass artists, including neon-glass artist Eve Hoyt, and Chicago glassblower Joe Ivacic. The idea, says museum glass coordinator Holly Smith, is to show that today's glass-pipe-makers are as artistically relevant as traditional glass artists.

"We believe pipes and their makers should be acknowledged similarly to other craftspeople and artists, as their work reflects our culture and trends as just as thoroughly," she says. "Our museum highlights glass artwork as a symbol of perseverance, freedom, and beauty, including the functional and controversial, so naturally we are honored to help shine a light on this group."

Opening reception 5:30 p.m. Friday; exhibit runs through May 7, National Liberty Museum, 321 Chestnut St. Free with admission, 215-925-2800, www.libertymuseum.org.