Last Monday evening, Scottish fiddler Alasdair Fraser and cellist Natalie Haas brought their extraordinary musical partnership to Washington for a large and appreciative crowd at the Institute of Musical Traditions. This is the 20th year Fraser and Haas have played together, and the anniversary gave the duo the excuse to return to their back catalog. And it is a masterful body of work, beginning with the album where I first heard them—their inaugural CD Fire & Grace, a project that turned heads worldwide with its exquisite musicianship and clear sense of joy. Steeped in different backgrounds— Alasdair from the roots world of Scottish fiddle and Natalie from the classical halls of Julliard—these amazing musicians responded to each other and to each intricate twist and turn of the music for a delightful two hours. It was art as a life-giving force. And they clearly had fun, recognizing the unique nature of the evening’s setting when they played the “appropriate for Washington” reel Little Donald in the Pigpen. Haas’s percussive use of the cello underpinned the magnificent …