"All museums would like to be free, but someone still has to pay the bills."
And there are special circumstances in Chicago that make going free less enticing than in cities with smaller institutions and fewer tourists, said Anderson. Along with art museums in New York, LA and San Francisco, he put the Art Institute in the very small "basket of institutions that have unusual access to high-net-worth, large-scale audiences, including tourism."
So where Dallas, with annual expenses of about $28 million, was drawing 2.7 percent of its operating income from general admission, at the Art Institute, the figure is more like 11percent of a budget that's over $100million. It would take an awful lot of big gifts to replace $11.8 million annually.
"We took that 2.7 percent risk," Anderson said. "We said the arithmetic isn't worth our current policy if the impact of going free could be so much more valuable to us."
Debra Kerr, a former Shedd Aquarium executive and local museum consultant, said, "We are all sort of watching Dallas to see what happens. I'm just not sure that every museum can sustain (being free). The aquariums are really, really expensive to operate." (Shedd's operating expenses were $56.2 million in 2013; it took in $33.8million in admission revenue.)
And, she added, "Tourists are not price sensitive" in the same way that local visitors are.
The Hammer Museum in LA was able to go free by getting two donors to back free admission for four years with a $2 million gift. It is already seeing payoffs in the first half-year.
"We're noticing a 25 percent increase in attendance since going free," said Samuel Vasquez, director of events and visitor experience. "Ethnic diversity has been something you can notice any time you come to the Hammer now."
It's been good for morale too.
"It makes people proud that we are an open platform for visitors," said Christopher Mangum-James, assistant manager for visitor experience. "Having that identity has really resonated among the staff."
Along with the new admission policy, the Hammer made its galleries friendlier, shifting security personnel, formerly in blazers, to T-shirts and more of an informational role. And there's a new way to become a member; instead of paying for it, guests tally 12 visits in a year.
In other words, going free is not just about taking down the turnstiles. Dallas instituted a system that awards points for scanning a member card in galleries, thereby providing valuable new data on how visitors spend their time at the museum.
Being free just makes a place different, said Bell, of Lincoln Park Zoo.
"Donors have said to me, 'Well, have you thought about just charging a quarter, even?'" Bell said. "I don't care if you charge a dime. It is still a charge. Free is different than any amount of money you might charge. ... And a lot of people will support this institution because it is free."
In Chicago's Pilsen neighborhood, another art museum has learned that being free can pay.
"We've always been free," Tortolero said. "When I started the museum, there were three things people told me I was crazy for: one, doing a museum in a working-class neighborhood; two, starting an arts museum in a working-class neighborhood; and, three, being free. They told me it couldn't be done. Twenty-seven years later, we've done it."
Not charging works on multiple levels, he said. First, it helps ensure diversity.
"I remember one time I was here with some European writers, and an African-American group walked out, and a Chinese group walked in, and the writers were just scratching their heads," said Tortolero.
While you think it would put pressure on the budget, it actually helps the fundraising. The museum's sponsor list is packed with big corporate names such as Target, Allstate and Sara Lee.
"A lot of foundations, corporations support this policy," he said. "It doesn't change our fundraising; we are super-aggressive. It just changes who we get funds from."
And there is one benefit being free provides that just might be the most enticing of all.
"We never have any complaints," Tortolero said. "If people don't like it, they can leave."