Mirror
Mirrors were polished surfaces (often glass backed with silver, aluminium or mercury)[source needed] which cast reflections. Some mirrors exhibited unusual properties.
In 1866, Edward Waterfield and Theodore Maxtible experimented with static electricity and mirrors in an attempt to develop time travel. (TV: The Evil of the Daleks) Another time machine that used mirrors was developed by General Mariah Learman in the early 21st century. (AUDIO: The Time of the Daleks) Rhian Salmond had a great aunt who time-travelled through powered mirrors. (PROSE: The Book of the Still)
In a parallel world, UNIT used mirrors and the Doctor's TARDIS to create a Lodestone and send Donna Noble back in time. (TV: Turn Left)
Tharils and Mirrorlings could use mirrors to travel to different dimensions. (TV: Warriors' Gate, COMIC: Mirror Image)
Mirrors were harmful to some life forms; they were used to defeat the Gorgon on Zeno, (COMIC: The Gaze of the Gorgon) another Gorgon on Earth, (TV: Eye of the Gorgon) Medusa in the Land of Fiction (TV: The Mind Robber) and the Mara on Deva Loka. (TV: Kinda) The Borad banned mirrors during his reign over Karfel. (TV: Timelash)
The Tenth Doctor punished Daughter of Mine by trapping her in every mirror. She was said to be the strange movement seen out of the corner of the eye when looking in a reflective surface. (TV: The Family of Blood)
The legendary Mortal Mirror of Castle Extremis was a portal to a parallel universe. Those who passed through it and were observed by someone on their side became trapped in the other realm, only able to return to their own reality as fragile beings made entirely out of glass. (PROSE: Martha in the Mirror)
The Fifth Doctor was able to trap the Mara in a Circle of Mirrors, (TV: Kinda) but the Mara was able to re-possess Tegan and communicated with it via a mirror, being able to as there was no circle. (TV: Snakedance)
The Saturnyns' use of perception filters meant that mirrors would not show their reflections, (TV: The Vampires of Venice) while the Krafayis could only be seen in mirrors. (TV: Vincent and the Doctor)
Susan discovered a full-length mirror in the TARDIS wardrobe which reflected a pale-skinned young man with fangs. (PROSE: The Exiles) Later, Ace discovered this same mirror and the same reflection of the young man. (PROSE: Echo)
The Second Doctor looked into a mirror to see what he looked like after his regeneration. At first he saw his new face with dark hair and green eyes, but the image wavered and momentarily became the First Doctor's. (TV: The Power of the Daleks)
Mirrors were also heavily involved in superstition. Humans, at least, believed that one would get seven years bad luck for breaking a mirror. The Tenth Doctor remarked on this upon realising that he had trapped himself in the past by breaking a mirror serving as a time window, except in his case it was 3000 years since he had come from the 51st century. (TV: The Girl in the Fireplace)
During the Siege of Trenzalore, the Eleventh Doctor used a mirror to freeze a Weeping Angel by forcing it to look at its own reflection, writing "with love from the Doctor!" on it. (TV: The Time of the Doctor)
The only way Bill Potts was able to see her true cyber-converted self was by using a mirror. (TV: The Doctor Falls)
