The 1,600-year-old cup from ancient Rome exhibits a mesmerizing emerald green color when light shines from the front and transforms into red when illuminated from the back.
According to Ancient Origins, the Lycurgus cup, dating back 1,600 years, depicts the figure of King Lycurgus of Thrace in ancient Rome. The British Museum has owned this cup since the 1950s, yet they have yet to uncover the reason behind the cup’s color-changing properties based on the light source.
Subsequent research has confirmed that the color-changing effect of the cup is due to interference, which occurs when light interacts with metallic nanoparticles. Today, this technology is used to create three-dimensional images using tiny silver particles. Consequently, the amount of information stored in optical digital devices (such as sensors, projectors, and medical imaging equipment) can be doubled.
The Lycurgus cup at the British Museum. (Photo: Wikimedia Commons).
According to a study published in the Proceedings of the National Academy of Sciences in July 2014, the interference phenomenon created by the interaction of light with nanoparticles allows three-dimensional images to surpass the conventional limits of diffraction—a process that causes waves to spread or bend when encountering an aperture or obstacle.
When metallic particles reach the nanoscale, they emit shimmering colors, and the Lycurgus cup is the first known instance to utilize this technique. Created in the 4th century, this glass cup is coated with finely ground silver and gold particles sized at 50 nanometers, smaller than one-thousandth of a grain of salt. It produces an optical phenomenon known as dichroism, meaning the color of the cup changes from green to red depending on the position of the light source.
Scientists suggest that the Roman artisans who created the dichroic effect in the Lycurgus cup did so unintentionally. However, some argue that the cup’s exquisite craftsmanship makes it unreasonable to claim it was merely a coincidence.
In fact, the precisely mixed ratio of metals indicates that the Romans had achieved a “mastery of craftsmanship” in using nanoparticles, commented Ian Freestone, an archaeologist at University College London.
Only in the last 20 years have scientists begun to understand the phenomenon present in the Lycurgus cup. However, they have not yet succeeded in applying this creative technique.
The technique for creating multicolored three-dimensional images. (Photo: Yunuen Montelongo).
To apply this in modern optics, an interdisciplinary research team has created an array of nanoscale metallic nanoparticles to produce multicolored three-dimensional images resembling the effect of the Lycurgus cup.
This breakthrough could reduce the size of many optical devices, which are typically quite bulky, according to Yunuen Montelongo, a researcher in the Department of Engineering at the University of Cambridge.
Using only a thin layer of silver, Montelongo and colleagues produced colorful three-dimensional image prototypes containing 16 million nanoparticles per mm2. Each nanoparticle is about 1,000 times smaller than the width of a human hair, scattering light into various colors depending on its specific size and shape. The scattered light from each nanoparticle interacts and combines to create images.
At that time, this discovery sparked astonishment but also skepticism. Many scientists denied the possibility that, 1,600 years ago, artisans with no knowledge of nanotechnology could develop such an advanced product. Even if they had knowledge, the technology of that era was still too primitive to support the production process. Creating such tiny metallic particles would require extraordinarily specialized machinery.
Moreover, the precise combination of metals has raised further doubts. Nevertheless, despite the skepticism, one truth remains: this cup dates back 16 centuries and, more importantly, it truly belongs to the ancient Romans.
It is astonishing to think that the Romans over a millennium and a half ago could understand and utilize nanoparticles at that time—a technology that modern humans have only discovered and utilized in recent decades.
