Suramya's Blog : Welcome to my crazy life…

May 10, 2022

Using ancient techniques for adding secret images in bronze mirrors to hide images in Liquid Crystal displays

Filed under: Emerging Tech,Interesting Sites,Science Related — Suramya @ 1:28 AM

There are a lot of things that were accomplished by our ancestors that seem like they should be impossible and this is why the theory that aliens were involved in our past to give us a boost is so popular. People don’t realize that just because it wasn’t possible in the western world doesn’t mean that others in the world couldn’t do it. In this post I am going to talk about Chinese/Japanese Magic mirrors that were first created ~200BC but modern science was only able to explain how they work in 2005 when M V Berry published an paper describing the optics of how this would work.

The Magic Mirror is a type of mirror that was popular in ancient china, specially the Han dynasty (206 BC – 24 AD). The specialty of these mirrors is that they were made out of solid bronze with the front side polished brightly so that it can be used as a mirror whereas the back would have a design cast in the metal. When a bright light was reflected by the mirror and shone against a wall the pattern on the back of the mirror would be projected onto the wall.

Example of how the Magic Mirror reflections look (Pic credit:

As you can imagine this is extremely hard to do. Due to trading with the Chinese, folks over in Korea and Japan have also been known to create these mirrors which are known as Makyō (magic mirrors) over there. One difference between Makyō and the Chinese mirror is that a Makyō doesn’t reflect the image on the back on the mirror when light hits it, nor does it have any obvious irregularities on its reflecting surface. But still it creates these fantastical images where nothing should be there. More details on how the mirrors were constructed and the history behind them are available here.

It took western scientists over 2000 years to figure out the science behind these mirrors, kind of.. as evident from the explanation below.

Although the surface of the mirrors is polished and seems completely flat, it has subtle convex and concave curves caused by the designed. Convex curves (outwards) scatter light and darken their areas of reflection. For their part, concave curves focus light and illuminate their areas of reflection. Mirrors are made of forged bronze, and the thickest parts are cooled at a different speed than the thin ones. Since the metal contracts a little as it is cooled, the different ranges of cooling “stress” or slightly deform the metal. The thin areas are also more flexible than the thick parts, so the polishing process, which should smoothen the metal until uniformity is achieved, exaggerates the slight differences in thickness. While we cannot see the pattern on the surface of the mirror, photos very clearly delineate it, so when they are able to bounce off the mirror’s curves, the pattern emerges.

Using the understanding gained from Berry’s paper Felix Hufnagel and his colleagues from the University of Ottawa in Canada to create a modern version of the magic mirror using liquid crystal which is a different state of matter (their molecules are both fluid and arranged in patterns). By applying an electric current to the liquid crystals they were able to tailor the orientation of the molecules which allowed them to create an image which would only show up when a particular combination of current/amplitude was applied. The images created using this technique look clear even when viewed from different angles which can be used to improve projectors for 3D images.

Their paper was published in Optica earlier this month and is an interesting (if confusing read).

Interesting links:
Wikipedia: Chinese Magic Mirror
Secret images hidden in mirrors and windows using liquid crystals

– Suramya

No Comments »

No comments yet.

RSS feed for comments on this post. TrackBack URL

Leave a comment

Powered by WordPress