We are grateful to Dr. Erich Schleier (written communication, 23 June 2003), Arch. Francesco Petrucci (written communication, 17 July 2003) and to Dr. Dieter Graf (verbal communication, 1 August 2003) for confirming the attribution to Gaulli from a transparency and black and white photograph.
Arch. Petrucci notes the apparent speed of execution and the strong painterly quality of the work early in Gaulli's career, circa 1670. He compares the way Saint Thomas is painted to the Seneca in the Chigi Assumption (Crespi Collection, Sao Paulo) and to the Beato Giovanni Chigi (Palazzo Chigi di Ariccia) documented circa 1671, and to a Saint Paul (Koelliker collection, Milan) of very similar dimensions.