Period-instrument performances no longer have the same power to shock that they did in the movement’s infancy, when their effect was akin to that of stripping centuries of grime off of old paintings. But they retain their capacity to augment and refocus what we hear in the music of the past.

A stellar example of this was the Handel and Haydn Society’s performance of Mozart’s Clarinet Concerto, on a Friday program led by guest conductor Richard Egarr. The piece was written at the end of Mozart’s life for the basset clarinet, a variant of the normal clarinet. The instrument — which H&H principal clarinetist Eric Hoeprich reconstructed two decades ago and played on Friday — looks something like a cross between a typical clarinet and an alto saxophone, and it has a deeper range than the standard instrument.