I'm still in the process of watching this, but what I've seen so far is fascinating. CASTING SHADOWS is a documentary produced by the defunct PBS affiliate WNYC-TV in 1987 to promote a new broadcast of the original episodes.
JONATHAN FRID introduces the proceedings, which also includes extensive interviews with Frid, KATHRYN LEIGH SCOTT, CLARICE BLACKBURN, JOAN BENNETT, NANCY BARRETT and LOUIS EDMONDS. It also includes some footage from a DARK SHADOWS FESTIVAL of the time.
Thanks to David-Elijah Nahmod for the link!