Fragments of glass from ancient Rome buried for thousands of years have formed crystals with sophisticated applications in modern tech, scientists say.
And these same ancient crystals can be used in modern technology to make lasers, filters, mirrors and even anti-reflection stealth devices.
Researchers found the pieces of broken glass rearranged and recombined with minerals over centuries to form photonic crystals, which can block certain wavelengths of light whilst allowing others to pass.
The study team, from Tufts University’s Silklab in Massachusetts, began their project by chance after visiting the Italian Institute of Technology’s (IIT) Centre for Cultural Heritage Technology.
Dr. Fiorenzo Omenetto, a professor of engineering at the Tufts University Silklab, explained: “This beautiful sparkling piece of glass on the shelf attracted our attention.
“It was a fragment of Roman glass recovered near the ancient city of Aquileia, Italy.”
Dr. Arianna Traviglia, director of the center, told Dr. Omenetto her team affectionately referred to the object as “wow glass.”
The research team soon realized they were looking at the natural nanofabrication of photonic crystals.
“It’s really remarkable that you have glass that is sitting in the mud for two millennia and you end up with something that is a textbook example of a nanophotonic component,” Dr. Omenetto admitted.
Chemical analysis dated the glass fragment to between the 1st Century BC and the 1st Century CE, with origins in the sands of Egypt – evidence of global trade at the time.
The majority of the fragment had preserved its original, dark green color, but on its surface was a millimeter-thick patina which had an almost perfect, mirror-like gold reflection.
Dr. Omenetto and fellow Tufts professor Dr. Giulia Guidetti used a new kind of scanning electron microscope that not only reveals the structure of the material, but also provides an elemental analysis.
“Basically, it’s an instrument that can tell you with high resolution what the material is made of and how the elements are put together,” Dr. Guidetti said.
The researchers found that the patina possessed a hierarchical structure made up of highly regular, micrometer-thick silica layers of alternating high and low density which resembled reflectors known as “Bragg stacks.”
Each Bragg stack strongly reflected different, relatively narrow wavelengths of light; with the vertical stacking of tens of Bragg stacks resulting in the golden mirror appearance of the patina.
Assessing how the structure formed over a period of around 2,000 years, the research team suggests a possible mechanism called “corrosion and reconstruction” might have played out patiently over centuries.
Dr. Guidetti said: “The surrounding clay and rain determined the diffusion of minerals and a cyclical corrosion of the silica in the glass.
“At the same time, the assembly of 100 nanometer-thick layers combining the silica and minerals also occurred in cycles.
“The result is an incredibly ordered arrangement of hundreds of layers of crystalline material.”
The research team said the photonic crystals have several applications in complicated modern technology, such as making lasers, filters, mirrors and stealth devices made from anti-reflection material.
Dr. Omenetto added that scientists may soon be able to grow optic materials in laboratories instead of manufacturing them.
He said: “While the age of the glass may be part of its charm, in this case, if we could significantly accelerate the process in the laboratory, we might find a way to grow optic materials rather than manufacture them.”
The molecular process of decay and reconstruction has some parallels to the eternal city of Rome itself.
The ancient Romans had a penchant for creating long-lasting structures like aqueducts, roads, amphitheaters, and temples, with many of these structures becoming the foundation of the city’s topography.
Over the next centuries, the city grew in layers, with buildings rising and falling with changes brought on by war, social upheaval and the passage of time.
In medieval times, people used materials from broken and abandoned ancient buildings for new construction.
In modern times, however, streets and buildings are often built directly on top of ancient foundations.
“The crystals grown on the surface of the glass are also a reflection of the changes in conditions that occurred in the ground as the city evolved: a record of its environmental history,” Dr. Guidetti said.
Produced in association with SWNS Talker