Mark Orton, the guitarist for Tin Hat, had only one objective when he helped to start the quirky chamber music ensemble whose music utterly defies categorization.

"Our one thing—as far as a mission statement goes—was that we didn't want to be a museum band." Simply put, that meant avoiding all established genres and focusing entirely on new compositions.

The group has more than achieved its goal. Eight years after its founding in the East Bay, the band has been challenging both fans and music writers alike to come up with the properly pithy hyphenated phase to describe its amalgamation of classical music, cowboy songs, jazz and Eastern European folk forms. Unfortunately, "Klez-Cow-Azz" won't pass the spell-checker test.

The group, whose list of influences ranges from Blur to Ligeti by way of Hank Williams, is one of the most interestingly orchestrated ensembles working today, featuring archaic guitars, violin, clarinet and just about every kind of keyed acoustic instrument produced in the 20th century, from prepared piano to pump organ and celeste.

"We are attracted to organic sounds," Orton explains. "The more character in that regard the better. The more pristine and slick a thing is, the less soul it has."

Following upon that philosophy, Orton prefers playing and composing on a range of antique guitars, including an old dobro and a diminutive vintage parlor guitar whose size is dwarfed by the modern dreadnoughts that most guitarists cart around. "I play the parlor guitar because of the technical fact that I do a lot of finger-style guitar without nails, so it is a lot easier to make these things speak."

"Besides," Orton continues, "they're easier to carry around."

Last year the group saw the departure of founding member Rob Burger, whose accordion and keyboard work anchored the ensemble with the kind of harmonic alacrity found on Mary Lou Williams' last couple of recordings.

Rather than a palace coup, or the standard "creative and artistic differences," the split was amicable. In fact, time zones had more to do with Burger's departure than anything. For several years the band functioned with Orton living in Seattle, violinist Carla Kihlstedt living in the East Bay and Burger living in New York. In Orton's words, "It was really tough to rehearse."

Joining the band upon Burger's departure were two phenomenally talented Bay Area musicians, Ara Anderson, on keyed instruments, and Ben Goldberg, on clarinet. "We didn't pick the musicians because of the instruments that they play," Orton says, "but rather who they are as composers, improvisers and musicians."

Orton is overjoyed to have Goldberg up onstage with Tin Hat. "Some of the things that we have tried to do—as far as combining jazz and classical music—he's been doing for years. He beat us to the punch. He's an inspiration."

And what about Anderson? A veteran of Tom Waits' group, he "brings a level of fun to the group." At a recent gig in Majorca, Anderson brought out children's toys to serve as percussion and spent the night "doing a kind of Art Ensemble thing with them."

Anderson's sense of jocularity will come in handy for the band's next engagement. After playing the Kuumbwa and a handful of gigs on the West Coast, they will set up a month-long residence at the Palace of Fine Arts in San Francisco with the Pickle Family Circus.

"It's not a pit orchestra situation," Orton insists. "We are integrated into the circus." So integrated, in fact, that the group is also bringing Matthias Bossi to provide Foley for the Circus as well as percussion for the band. Bossi is perhaps best known for his work with the avant-garde performance ensemble Sleepytime Gorilla Museum, whose ranks also feature Tin Hat violinist Kihlstedt. But the musical material Tin Hat is hauling out for this show is far less aggressive than Sleepytime's—it's a mixture of reworked tunes from their first four records and a smattering of new compositions that have come out of the new lineup.

Given all the musical ideas swirling about with the expansion of the band and its new projects, one is left to wonder if they are any closer to defining their sound in words. Fortunately, no. "If anything," Orton says, "it's a broader palette now."

Tin Hat plays Thursday, Dec. 1, at 7pm at Kuumbwa Jazz Center; 320-2 Cedar St., Santa Cruz. Tickets $12/adv, $15/door. (831.427.2227; www.kummbwajazz.org.)

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