Gold flecks make super-transparent glass fully opaque from one side

Glare-free windows could be made from a material studded with billions of tiny metal patches. This makes a one-way window that is matte – it looks opaque, reflecting barely 1 per cent of light from the outside – but still transparent, which could allow cars and offices to have privacy without blurring the view or significantly lowering the amount of light they let in.

Mu Wang at Nanjing University in China and his colleagues created a glass-like material that has a similar matte finish to frosted glass called a transparent matter surface (TMS). Unlike existing anti-glare coatings and films, you can look at or photograph an object through TMS without it looking blurry.

Wang says that being matte and transparent are typically mutually exclusive properties – to achieve both simultaneously, he and his team covered the material in nano-sized patches that scatter and reflect light in just the right way. They made these components from a reflective metal, such as gold, and materials like silicon that conduct electricity poorly, which reduces how much light they reflect. Then they arranged billions of them on a glass wafer.

They tested it by shining light on it and found that it can reflect as little as 1.3 per cent of light while still transmitting enough of it for a camera with a TMS wafer overlaid on its lens to take clear photographs. The researchers also combined it with a camera connected to an AI that labels objects and asked it to identify a tennis ball on the other side. The AI was successful when viewing the ball through the TMS, but labelled it as “unidentified” when viewed through the blur created by a conventional anti-glare film.

“What excited us most in our experiments was the fascinating moment that we first saw the freshly prepared 4-inch sample with our own eyes, without any special equipment. It was difficult to imagine how a material could be clear and undistorted when light passes through it but also have a hazy appearance when reflecting light,” says Wang.

Simon Horsley at the University of Exeter in the UK says this material is well suited to produce “quite large windows” and could be useful for reducing light pollution. Reflection is a big contributor to light pollution, and this material could minimise it as it reflects soft, diffuse light instead of a more bothersome bright glare.