The string quartet, all by itself, seems to contain an infinite range of colors within its limited spectrum. It deals largely in linear figures and subtle shades of gray. But the lines can vary in finesse from the heavy strokes of a cello's C string played with rich vibrato to the thin, other-worldly, almost nonexistent sound of harmonics played high on a violin's E string. Add shifting balances and varieties of attack, from a resounding pizzicato to the light notes that dance at the tip of a violin's bow, and you have an array of expressive resources that composers have hardly begun to exhaust in more than two centuries of the form's history.

Include a harp, piano, flute or clarinet, as the Emerson String Quartet did this weekend at the Renwick Gallery, and the colors and contrasts expand tremendously. The second half of the program stuck to the relative sobriety of the string quartet without additives -- though "sobriety" hardly describes Dvorak's energetically melodious, soulfully folk-flavored Quartet in A-flat, Op. 105, which the Emerson played brilliantly. In the first half, quartet members were joined by four of Washington's finest musicians -- harpist Dotian Carter, clarinetist Loren Kitt, pianist Lambert Orkis and flutist Sara Stern -- to explore studies in color composed by Debussy and Barto'k. This half of the program could have taken its title from Barto'k's "Contrasts," which were beautifully played just before intermission.

Stern opened the program unaccompanied, playing Debussy's "Syrinx" in the resonant acoustics of the foyer outside the darkened Grand Salon. The audience and performer were in different rooms with their backs to each other, and the darkness enhanced the disembodied quality of the sound that seemed to come from everywhere and from nowhere. Carter, a superb performer technically and musically, brought balance and vitality to Debussy's "Danse sacre'e et danse profane" and his Sonata for Flute, Viola and Harp.