Sketch for fresco by Il Volterrano, 1644. Notice the special attention to the left-hand grip by the artist..
Added another article to HubPages, How to Hold a Sackbut: The Grip of the Trombone in Pictures. The way the early trombone was held has performance implications, including where first position was, what key the instrument was in, etc. Check out the article, with its 33 historical images, here.