Dichroic, or two-coloured, materials have existed for ages, at least since the fourth century. These materials, primarily dichroic glass, can reflect, absorb and transmit light differently depending on the angle from which they are observed. Recently, Dutch researchers from Wageningen University have developed new dichroic materials for 3D printing. In addition to artistic value, these materials can also help to create optical filters.

The research team created materials using plastics and gold nanoparticles. This is an established technique, as exemplified by the stained glass windows created centuries ago. Now these researchers are applying similar principles to printing. Nanoparticles have been the basis for many materials in additive manufacturing, especially gold, making them ideal for this purpose.

Due to this, dichroic printed material displays two different colour palettes, depending on the light source and perspective. When light falls directly on an object, it appears dirty brown. However, when light falls on the other side, it becomes a transparent purple-pink. Scientists are still improving the technology, testing the effects of different types of nanoparticles and printed materials.

The material itself is simply PVA plastic for 3D printing, to which the researchers have added nanoparticles. Everything else is a trick of the light created by the presence of gold. Gold nanoparticles can be different in size, but a large amount is not needed for this effect. Only 0.07% of the weight of the material obtained is sufficient.

Such materials can be seen in art such as modern architecture, and may also be used in the field of optics. It would be quite interesting to have a look at the Bennu asteroid 3D printed using this material.