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When is a magical illusion not a magical illusion? When it’s a maths trick that will make you see the world in a new way.

A chance to discover anamorphism and create anamorphic images, Mirror Pillar will bring mathematical and geometrical thinking together with your own drawing skills to produce giant artworks across Manchester. Anamorphism is a technique that’s been around since the time of Leonardo Da Vinci, and involves distorting an image so it can only be seen correctly from a particular point (called perspective, or oblique anamorphosis), or using a special device like a curved mirror (called mirror, or catoptric anamorphosis).

Da Vinci’s artwork Leonardo’s Eye is one of the earliest examples of perspective anamorphosis. The artist Hans Holbein the Younger was known to include stretched images within his paintings, including ‘memento mori’ skulls which look correct when you stand at one side of the painting. Trompe L’oeil art techniques use realistic imagery to deceive the eye, but only when you’re standing in the right place—the church at Santa Maria presso San Satiro in Milan is one of the earliest examples of such a technique, with a short section of church which looks like it goes much further.

Mirror anamorphosis has also been used to hide images: an image of Bonnie Prince Charlie was disguised in a painted tray (kept in The National Archives), and only visible using a cylindrical mirror—at the time, keeping such an image would have been considered treason.

Using anamorphosis, beautiful transitory images can be created, which look stretched, wrong or even nonsensical if not viewed from exactly the right point. Modern artists have used anamorphic techniques to create stunning illusions, including Trompe L’oeil drawings on the floor which look 3D, images drawn across walls, floors and ceilings which resolve into perfect shapes when you walk across to exactly the right spot, and giant distorted sculptures which look perfect when viewed in a curved mirror.

The Mirror Pillar is a 2m high cylindrical mirror, which can be used to view images on the floor—there, the images will be stretched around into a large semicircle, but looking in the pillar they form a perfect square. We’re inviting people to use their artistic and mathematical skills to help create an image – by choosing one square from our grid, blowing it up to the right size, stretching it out around the curve and then mirroring it so it looks correct mirrored in the pillar (we’ll help, of course!). The squares we’ll be copying vary from simple ones with only a few lines or dots, to others containing complicated shapes that’ll need transforming correctly to view in the pillar.

The way the Pillar distorts images uses the fact that the Pillar is both a mirror, and a perfect cylinder. If you look at an image on the floor in front of a normal mirror, you’ll see the part of the image nearest your feet at the top, and the part of the image nearest the mirror at the bottom. This is because the angle light reflects off a mirror (the angle of reflection) is the same angle the light came in at (the angle of incidence). When you see an object, it’s because a ray of light that’s bounced off it comes to your eye, and if you’re looking at the object in a mirror, the light will have travelled from the object, bounced off the mirror and then gone to your eye.

In the case of a curved mirror like the Mirror Pillar, if you’re looking at a point straight in front of you that’s dead centre on the cylinder, the reflection will work in exactly the same way as for a flat mirror – the light bounces off vertically. But if you look to one side, which part of the image you’ll see is slightly harder to predict – the light ray will bounce off the mirror at a different angle, because the piece of mirror it’s bouncing off is angled away from you, so the light reflects further round and the image spreads outwards. It’s possible to calculate the angle the light will bounce off at, if you know the angle you’re looking at the mirror horizontally and vertically, the diameter of the cylinder, and the height of your eye.

For our Pillar images, we’ve already calculated where the edges of the square go, and you’ll be given a blank shape to fill in with the right picture. But everything in the middle of the shape is up to you – you’ll need to reflect it and stretch it horizontally. We’ve got erasers if you want to make sure you’ve got it right, then you can go over the lines with a marker pen and add your square to our giant image. We’ll also have other activities you can try – creating your own image using a mini-Mirror Pillar, making a sculpture around the mini-Pillar using plasticine, or even using a projector to create your own perspective anamorphism. Come and find us in a variety of locations across four days of MSF, or take a look at the Mirror Pillar website to try some of the activities at home or school.

Mirror Pillar is at locations around Manchester from 20 October to 23 October. Click here for more information.

Images courtesy of Sheamol Obeda.

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