More than 100 would-be listeners were turned away from the standing-room-only concert by Libba Cotten and Mike Seeger at the Museum of Natural History Saturday night. The lucky ones who got inside were treated to bluesy ragtime guitar-picking and an impromptu song workshop and wisecracking storytelling by Cotten, who turned 90 last week.

It wouldn't be honest to ignore that age has slowed Cotten's fingers and cracked her voice. The canny performer found ways to get around her infirmities, however. She simply slowed the pace of her guitar work so that her distinctive phrasing remained as sharp and charming as ever. Cotten demonstrated her signature style of alternating high melody and low bass notes on her most famous song, "Freight Train," which thousands of folk guitarists have learned over the years. This and her other original tunes--both reverent hymns and irreverent blues--were marked by captivating melodies and clever turns of phrase. Because her voice can no longer do justice to her striking melodies, she quickly taught each song to the audience, and the good voices in the Folklore Society of Greater Washington gave her tunes a rich, choral treatment. At the end of the show, Cotten brought out her granddaughter and then her great-great-granddaughter to sing her lyrics as she played guitar.

Mike Seeger, who was just a child when Cotten worked for his parents, opened the show with dazzling dexterity as he played old country songs on one instrument after another: guitar, banjo, fiddle, jaw harp, mouth harp and autoharp.