Now one of the commonest tunings in clawhammer style, above all for playing with "D" fiddle tunes. Also used by Tony Ellis in many of his lovely bluegrass-cum-old-time 3-finger style tunes, and perhaps by other bluegrass musicians. For all I know, this tuning may have a history reaching at least as far back as the Standard-C (gCGBD) recorded in so much of the 19th C literature. Blanton Owen's liner notes for "Old Originals Vol 2" say that the Virginian Stuart Carrico considers the Double-C tuning to be older than the Standard-C. (Stuart was born at the turn of the century.) Tuned up to D, this becomes aDADE. Tuned down to B-flat, fBbFBbC."