Potent, Low-Key Indigo Girls Cement Bond

While Jewel was still up in Alaska, the Indigo Girls delivered a lilting, country-steeped tune called “Closer to Fine.� Ever since, the Atlanta folk-rock duo’s career has struggled to top the down-home heart and living-room spirituality of that minor 1989 hit, even though the team has stretched in both its music and its ideology.

On Wednesday, the Indigo Girls opened a two-night Greek Theatre engagement with a chummy, low-key concert that revealed why their music remains potent for longtime fans--and why that fan base remains relatively small.

With their stage loaded with mandolins, percussion, violins and a piano, Amy Ray and Emily Saliers are clearly unafraid to move beyond the standard acoustic guitar. Starting out strong, they launched into two of the more striking songs on the Indigo Girls’ current and sixth record, “Shaming of the Sun�: Saliers’ folky, upbeat “Get Out the Map� and Ray’s darker-edged “Don’t Give That Girl a Gun.� The singers played up the contrast between Ray’s deep-throated alto and rock sensibility and Saliers’ sweeter voice and folkie bent and harmonize with delicious beauty.

But by the middle of a set peppered with can’t-miss tunes--Bob Dylan’s “Tangled Up in Blue,� Bob Marley’s “Redemption Song�--the Girls began to lose their lyrical punch and musical muscle. The group gained ground only with “Scooter Boys,� an uncharacteristically fierce new song.

This is folk-rock’s big year on MTV, but the Indigo Girls speak to a tight-knit, insular crowd that doesn’t demand the stylish, urbane chic of, say, k.d. lang. Although the new album lacks radio-ready hooks and its lyrics are sometimes irritatingly vague, Wednesday’s show revealed that the Indigo Girls’ blend of humility, heart and passion for music will remain a lure for its devoted fans.