Researchers have discovered that x-raying paintings may reveal unusual details, such as areas that were painted over. In the case of John Dee performing an experiment before Queen Elizabeth I, by Henry Gillard Glidoni, a famous painting of the scientist and occultist at work, some startling changes in tone are seen.
X-Ray reveals that before it was painted over, Dee stood in a circle of skulls to perform his ritual.
Other features appear to have changed, such as the removal of various glassware.
Why were these changes made? Were they trying to downplay the occult nature of what Dee was demonstrating? Did the artist feel that it was just too grim?