Christopher Whitby points out that there are subtle differences between the crystallomancy that Dee advocated, where the scryers used a crystal stone to see visions, and the scrying that used mirrors, known as
catoptromancy. While in
catoptromancy visions can be seen that do not involve the agency of angels or other spirits, all known examples of crystallomancy do include the appearance of divine assistants such as Dee's angels.(20) Dee possessed at least three different stones: a "great Chrystaline Globe," a crystal sphere mounted in a wooden frame, and a stone that the angels delivered to him.(21)