When Jack White recruits a tiny local band for his Third Man label, he intends an immaculate conception; no one is permitted to know how and why he zooms in. Tamara Finlay of one such Michigan band, a folk duo called the Thornbills, had the audacity to question White about what led to the spontaneous e-mail asking them to record a single. Before he turned and left the room, White's reply was a simple "I don't feel comfortable disclosing my sources." His whims, which can shake and alter lives, aren't for public analysis.

Finlay and Jim Wiegand III, cousins and multi-instrumentalists, can't stop laughing when they tell that story. It's about more than just White's standoffish ways. The particular absurdity of being mysteriously championed by the man who restored Detroit to its place on the rock 'n' roll map is a twist in the Thornbills' bio that still seems implausible, especially to them. Jack White's been on the cover of Rolling Stone hobnobbing with Keith Richards, but he's also been in a control room fine-tuning stark Russian-language ballads with this two-piece, based in Livonia and Ann Arbor.

The Thornbills' traditionalist, earthy acoustic folk doesn't fit much of a rock 'n' roll mold, on record or in their hushed live performances. On stage, they chat with familial ease, casting the occasional nervous glance into the audience. Finlay switches from an autoharp to a dulcimer, Wiegand makes a low-key joke, and then suddenly they are playing music. It is the wonder of unheralded talent — instead of recapturing a moment, their performances still feel lived-in and vital.

Both Michigan natives, Wiegand, 29, and Finlay, 31, grew close as children when their respective parents divorced. Without ever actually talking about it, Finlay says, they bonded as fellow misfits over the shared experience. "We both got picked on in school and were kind of moody. We used to get together and run amok on our uncle's farm in the summers, riding horses, catapulting G.I. Joes into the pond, making music videos dressed as Wayne and Garth, sustaining all kinds of injuries from dumb reckless stunts."

The pair had each been in several bands separately before forming the Thornbills two years ago as an outgrowth of a project of Wiegand's that Finlay provided harmonies for. It was a fruitful alliance; both immediately put other endeavors on hold. The songwriting came naturally, first with Finlay arranging Wiegand's ideas, then "our perspectives kind of melded," Finlay recalls. "It turned out we were incredibly similar."

"Whatever one of us is lacking," Wiegand explains, "the other fills in the hole."

Finlay adds, "Neither one of us on our own really functions normally as a human being or a musician."

Wiegand summarizes: "We are the black sheep."

The new Third Man single, which was actually released in November — but is celebrated this week with a show in Detroit — is a sonic leap forward, a result of White's detail-amplifying production.

"Uncle Andrei" is a Russian waltz that betrays little modern influence; when the vocals begin, the impact is immediate. Most rock bands tackle non-Western music as a kind of stylistic, theatrical goof. Finlay's empathetic singing and the purity of the performance allow no doubt of the song's sincerity. There's a reason.

She lights up when asked about the absence of strain in her Russian-language vocals that tinge "Andrei" and dominate "My Star" (the bonus track offered by Third Man on the digital single). "My mother is Ukrainian," she reveals. An early involvement in Ukrainian choirs lent her a fixation on Russian musical traditions. Her grandfather inspired "Uncle Andrei": "He told us about the old country, and it ignited a passion to embrace the culture. That's second nature to me. It isn't a foreign language; it's a part of my personality." The band even holds its daily two-hour practices in her mom's basement in Livonia, surrounded by artifacts of her background, including "Ukrainian kitsch and knickknacks and folksy paintings all over the walls."

"Andrei" illustrates the depth of the duo's partnership: Finlay couldn't finish the song. She explains, "I came to Jim saying, 'Help me say this about my grandfather and my upbringing,' and he really took the helm." The musical process was just as collaborative. "'Uncle Andrei' was my imitation of what I thought a Russian song would be," Wiegand says. Finlay gathered up a sampling of traditional Eastern European folk and asked him to help her construct the song. He came back with something less florid but still gripping.

The Appalachian-tinged flipside "Square Peg" also conveys some family history, this time about the cousins' shared relatives; their aunts and uncles performed together frequently in Carter Family-like collectives. But the Thornbills won't have you pigeonholing them as revivalists. "The fact that we come off as folk was kind of an accident," Wiegand concedes. As Finlay puts it, "We don't strive to be genuine. We just don't know how else to be."

It all happened rapidly; in just a couple of years, open-mic gigs at A.J.'s Cafe in Ferndale with two-song sets gave way to tri-color Third Man vinyl. It isn't that these two are starstruck over White's interest in them so much as they are cautious — the future remains uncertain. Third Man hasn't sprung for anything beyond a 7-inch so far. The Thornbills watch what they say about a potential big break and, in case it isn't so big, mostly keep any budding ambitions in check. They're careful about the image they project too; Finlay accents points she thinks are important to understanding the Thornbills. Third Man doesn't invest even this much time in just anyone, and the band carries the weight of that responsibility for now, whether the relationship continues or not.

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