A crystal ball is a crystal or glass ball believed by some people to aid a psychic to see other places and possibly, other times.
Magda Rakosi, a gypsy fortune teller in the service of Edith Collins, often used a crystal ball (701). She was using her crystal ball one day, in 1897 to search for the Collins family jewels when she first came in contact with Barnabas Collins, who needed help to be released from his coffin (701). After her powers were stolen by Count Andreas Petofi, she was saddened that not even her crystal ball would show her what she wanted (801).
In 1967, Burke Devlin gave David Collins a crystal ball as a gift (48) to the horror of his father and Aunt Elizabeth (54). David, always imaginative, seemed to be able to see some things, but whether this was his imagination or not was always hard to tell. He claimed that he learned in the crystal ball that someone was trying to kill Vicki, and that his cousin Carolyn would never marry Joe (53).
He tried to use to the crystal ball to solve the disappearance (48) and murder of Bill Malloy (59) and pretended to use it to discover the whereabouts of his governess, whom he had locked in a secret room in a locked wing of Collinwood (86). He used it again to locate Sarah Collins (310).
In episode 701, there appears to be an inscription (signature?) on the front of the ball, most easily seen just after the view within the ball passes thru the gate of the mausoleum.