Pianist Alexander Wu has anchored All4One’s endeavors for four years or so, but Sasha Papernik, his collaborator for this program, is a new musical partner. (Christopher St. Clair)

Piano-four-hands performance, in which two people play side by side at the same keyboard, was big in 19th-century parlors, where people entertained themselves and one another with transcriptions of symphonies and other large-form tidbits. Today, such duos surface in concerts from time to time, and one such pair, traveling under the name All4One, offered an afternoon of light-hearted entertainment Sunday at the Smithsonian American Art Museum’s McEvoy Auditorium as part of the Steinway Series.

Pianist Alexander Wu has anchored All4One’s endeavors for four years or so, but Sasha Papernik, his collaborator for this program, is a new musical partner. The two seemed to be ironing out kinks in their ensemble. When they played on their own — Papernik with lightly transparent performances of Chopin and Scriabin, and Wu with exuberant Earl Wild etudes on Gershwin songs and the dreamy Ellington “Reflections in D” — they sounded assured and settled.

Together, they are working out what they want to do with the music. Ornaments in the Mozart “Eine Kleine Nachtmusik” transcription need thinking through. Rhythmic subtleties in the delightful set of waltzes by Valery Gavrilin haven’t yet jelled, and the Otto Singer arrangement of the theme from Bizet’s “Carmen” needs a lot more pizzazz.

But all this is doable, and Wu and Papernik are an uncommonly attractive and entertaining pair. Their introductions to each piece were handled beautifully. They managed a comfortable balance of the formal and the casual, and the large audience that lined up early to fill the hall loved it all.

Reinthaler is a freelance writer.