How to Make a True Mirror: Two Mirrors at a Right Angle
A true mirror, also called a non-reversing mirror, shows your face the way other people see it instead of the left-right reflection every ordinary mirror gives. You can build one in a quarter of an hour from two flat mirrors, and the design has not changed since it was patented in 1887. This guide covers the materials, the five steps, the one check that matters (the angle), why a dark seam appears and how the commercial version hides it, and the history from the Hooker patent to a curved mirror computed at Drexel. If you only want to see the effect, the free true mirror in your browser does it with your camera, no build and nothing uploaded.
Key Takeaway
Two mirrors meeting at exactly 90 degrees, reflective faces inward. Look into the corner. The second reflection undoes the first, so left stays left.
How a True Mirror Works
A flat mirror does not swap left and right so much as front and back: the light from your left eye comes straight back to your left, so the image's left eye sits where a facing person's right eye would be. Add a second mirror at a right angle and the light from your left side bounces off one mirror into the other and comes back on your right. The reversal happens twice and cancels. You see yourself as someone standing in front of you does, live and moving, which no photograph can show.
What You Need
- Two flat mirrors of the same height, 20 to 30 cm tall is plenty for a face (tiles, locker mirrors or two halves of one cheap mirror)
- A true right angle to set them against: a hardback book, a set square or the corner of a sturdy box
- Strong tape, a small hinge or a wooden V-block to hold the angle
- Optional: two first-surface (front-silvered) mirrors, which join with a far thinner seam
The Build in Five Steps
Step 1
Stand the two mirrors edge to edge
Reflective faces inward, forming an inside corner like an open book. Butt the edges together with no gap; a strip of tape along the back edge makes a hinge, or sit them against the corner of a box.
Step 2
Set the corner to a right angle
Press a book, a set square or any true 90-degree corner into the inside of the V and close the mirrors onto it. This is the whole trick: the second reflection only undoes the first at exactly 90 degrees.
Step 3
Check with a straight line
Hold a ruler or a pencil level across the front of both mirrors. Its reflection should run as one unbroken line through the seam. A kink at the seam means the angle is off; nudge one mirror until the line is straight.
Step 4
Look into the corner from arm's length
Centre your nose on the seam. The two mirrors each show half of your face, and because the light has bounced twice, the halves are on the sides other people see them. Wink your left eye: the eye that winks back is on the right of the image, as it would be on a person facing you.
Step 5
Read the test and keep the seam vertical
Hold a page of text up to the mirror: it reads the right way round. Tilt the assembly and the image turns through twice the angle, so keep the seam upright. Expect a dark line down the middle with ordinary mirrors; it is the glass in front of the silvering, not a mistake.
Why the Seam Shows, and How the Real Thing Hides It
An ordinary mirror is silvered on the back, behind a sheet of glass a few millimetres thick. At the corner the two sheets of glass meet before the two reflecting layers do, and that gap shows as a dark double line down the middle of your face, exactly where the seam lands on your nose. Three things reduce it: thinner mirrors, bevel-free edges pressed hard together, and first-surface mirrors, which carry the coating on the front of the glass so the two reflecting layers can meet at the corner. First-surface corner mirrors are what the True Mirror Company sells and what museums install as the non-reversing or antigravity mirror. For a home build, a one or two millimetre line is normal and your eyes stop noticing it within a minute.
One more property to expect: the image rotates through twice the angle you tilt the assembly. Lean the corner ten degrees and your reflection leans twenty. Keep the seam vertical and the mirror flat on a table or shelf.
What You Will Notice, and Why
Most people's first reaction is that the face in the corner looks slightly wrong, and the reason is familiarity rather than looks. Every face is a little asymmetric: one brow sits higher, the smile pulls to one side, the hair parts on one side. In an ordinary mirror those asymmetries are where you have always seen them. In the true mirror they swap sides, and the brain flags the change. In the 1977 experiment by Mita, Dermer and Knight, people preferred the mirror-image print of their own face while their close friends preferred the true print; the two biases ran equally in both directions. A 2021 study in Aesthetic Surgery Journal (Frautschi, Orfahli and Zins) repeated the comparison with 30 people and a non-reversing mirror: 83% saw a difference and most rated themselves lower in the true view. Nobody else sees that difference, because they only know the true face. If you want to know what actually differs between your two sides, the free face symmetry test measures it instead of leaving you to stare.
A Short History of the True Mirror
- 1887
- John Joseph Hooker is granted US patent 370,623, Mirror for Obtaining True or Positive Reflections: two flat reflecting surfaces set at an exact right angle, so that the second reflection corrects the reversal of the first. The home build on this page is his drawing.
- 1977
- Mita, Dermer and Knight publish the mirror-image study in the Journal of Personality and Social Psychology: people prefer the reflected print of their own face, their friends prefer the true print.
- 1992
- John Walter begins making and showing the True Mirror, a first-surface corner mirror with an almost invisible seam; the company says it has been installed in more than 30 museums.
- 2009
- R. Andrew Hicks, a mathematics professor at Drexel University, designs a non-reversing mirror from a single curved surface, computed so the distortion of a curved mirror cancels the left-right swap without a seam.
- 2021
- Frautschi, Orfahli and Zins, in Aesthetic Surgery Journal, have 30 people rate themselves in a standard and a non-reversing mirror: 83% saw a difference, and self-ratings of age and appearance were lower in the true view.
Sources: US patent 370,623 (Google Patents); Mita, Dermer and Knight, Journal of Personality and Social Psychology 35(8), 1977; the True Mirror Company's own history page for the 1992 date and the museum count; Drexel University's 2012 announcement of the Hicks mirror; Frautschi, Orfahli and Zins, Aesthetic Surgery Journal 41(12), 2021.
Frequently Asked Questions
What angle do the two mirrors need to be?
Exactly 90 degrees, reflective faces inward. A few degrees off and the two halves of your face no longer meet at the seam: one half sits higher or wider than the other. Set the corner against a book or a set square, then fine-tune by looking at a ruler held across both mirrors until its reflection is one straight line with no kink.
Is a true mirror really how other people see you?
In orientation, yes. A flat mirror swaps left and right, so the face you know has your right eye on the left of the image. Two mirrors at a right angle reflect the light twice, and the second reflection undoes the swap, so you see the unreflected face everyone else sees, moving and in real time. It is still a mirror: distance, lighting and expression are the same as in any mirror.
Why does my face look wrong in a true mirror?
Familiarity. You have seen the reflected version for years and almost never the true one, and people prefer the version of a face they have seen most. In the 1977 study by Mita, Dermer and Knight, people chose the mirror-image print of their own face while their close friends chose the true print. Your asymmetries swap sides in the true view, so your brain reports them as new. Nobody else has that reaction; they only know the true face.
Does text read the right way in a true mirror?
Yes. Hold a page up to the corner and the words read left to right, which is the quickest check that the build is working. In an ordinary mirror the same page reads backwards.
Why is there a dark line down the middle?
Ordinary mirrors carry their silvering behind a sheet of glass, so the reflecting surface sits a few millimetres back from the front. At the corner the two sheets of glass meet before the two reflecting surfaces do, and that gap shows as a dark double line. First-surface mirrors (the coating on the front of the glass) can be joined almost invisibly; that is how the commercial version hides the seam.
Can I make a true mirror from my phone instead?
You do not need to build anything to see the effect. A phone's front camera already captures the unreflected face; the preview is flipped to feel like a mirror. The free true mirror on this site shows the live camera un-mirrored in your browser, with a flip to compare and both halves of your face doubled, and nothing is uploaded. Some camera apps also have a mirror toggle for the preview.
Can you buy a true mirror?
Yes. The True Mirror Company, founded by John Walter, has sold a first-surface version since the 1990s, and large two-mirror corner installations appear in science museums under names like the non-reversing mirror or the antigravity mirror. A home build with two ordinary mirrors costs a fraction of that and shows the same effect, seam included.
See the effect without building anything
The same two reflections, done by your camera in the browser. Nothing is uploaded.
True Mirror
FreeYour live camera un-mirrored, a flip to compare, side by side, and each half of your face doubled on your own midline.
Face Symmetry Test
FreeTwelve landmark pairs across your midline, a score, and where it sits among tens of thousands of faces.
Online Mirror
FreeA plain webcam mirror with full screen, zoom and a light, and a true-view toggle.