Zoom in / Microscopic view of photonic crystals on an ancient Roman glass surface.
Julia Guidetti
Nature is the main creator of nano. The latest evidence of this is an unusual piece of ancient Roman glass (called “dazzling glass”) that has a thin coating of gold. Roman glass shards feature blue, green and orange iridescent colors and are the result of a corrosion process that slowly restructures the glass to form… Photonic crystalsThe glistening, mirror-like gold luster of this shell is a rare example with unusual optical properties, it says New paper Publicēts Proceedings of the National Academy of Sciences.
This is another example of naturally occurring structural color. As mentioned above, the bright iridescent colors in butterfly wings, soap bubbles, opals, or beetle shells do not come from pigment molecules, but from their naturally occurring structure. Photonic crystals. In nature, for example, chitin shells (a polysaccharide commonly found in insects) are arranged like roof tiles. Basically, they form a Diffraction gratingExcept that photonic crystals only produce certain colors or wavelengths of light, while a diffraction grating would produce the entire spectrum, just like a prism.
Photonic crystals, also known as photonic bandgap materials, are “tunable,” meaning they are precisely arranged to block certain wavelengths of light while allowing others to pass through. Change the structure by changing the size of the tiles and the crystals become sensitive to a different wavelength. They are used in optical communications as waveguides and switches, as well as in filters, lasers, mirrors and many hidden anti-reflection devices.
Scientists can make their own colored structural materials in the lab, but it can be difficult to scale the process for commercial applications without sacrificing optical precision. Therefore, creating naturally occurring structural colors is an active area of materials research. For example, earlier this year scientists from the University of Cambridge developed An innovative new layer of plants becomes cooler when exposed to sunlight, making it ideal for cooling future buildings or cars without the need for an external energy source. The resulting films are colored, but they are structurally colored in the form of nanocrystals, not due to the addition of pigments or dyes.
Last year, MIT scientists adapted a 19th-century holographic technique invented by physicist Gabriel Lippmann to develop chameleon-like films that change color when stretched. These films would be ideal for creating dressings that change color in response to pressure, letting medical personnel know if they are packing a wound too tightly—an important factor in treating conditions such as venous ulcers, pressure ulcers, lymphedema, and scarring. Kids will love wearing the color-changing bandages, which make a great gift for pediatricians. The ability to produce large sheets of material opens up applications in clothing and sportswear.
Zoom in / A small gold flake from the surface of an ancient Roman glass specimen.
Fiorenzo Ominito and Julia Guidetti
Fiorenzo Ominito, a materials scientist at Tufts University who co-authored the new paper, discovered the unique fragment during a visit to the Italian Institute of Technology’s Cultural Heritage Technology Center and decided it was worthy of further scientific investigation. “What caught our eye was this beautiful piece of glass that sparkled on the shelf.” Umineto said. “It was a piece of Roman glass found near the ancient city of Aquileia, Italy.” The director of the center called it “blinding glass”.
Aquileia was founded by the Romans in 181 BC, initially as a military outpost, but soon flourished as a trading center trading in metal forgings, Baltic amber, wine and ancient glass. “The discovery of a wooden barrel with 11,000 pieces of glass in a Roman shipwreck in seawater off Aquileia demonstrates the city’s leading position in the exchange and processing of recycled glass along trade routes,” the authors write. At its peak in the 2nd century AD, the city had a population of 100,000. Its fortunes declined after it was sacked by Attila and the Huns in 452 and again by the Lombards in 590. Today, the town has only about 3,500 inhabitants, but it remains an important archaeological site.
During a field survey in 2012, archaeologists found the “dazzling glass” on the topsoil of an agricultural field, possibly brought to the surface by recent plowing, and were immediately struck by its characteristic multicolor. About 780 pieces of glass were collected at the same time, but they had the iridescent ivory color common in ancient Roman glass. Although this shell was generally dark green, it was covered by a millimeter-thick patina of gold that was almost mirror-like in its reflective properties. To learn more, Ominito and his colleagues subjected the shell to both optical microscopy and a new type of scanning electron microscopy (SEM), which reveals not only the material’s nanometer-resolution structure, but also its elemental composition.
Chemical analysis dated the glass from the first century BC to the first century AD. There were high levels of titanium, indicating that the sand used to make the glass was of Egyptian origin, which usually contains more impurities. As for the dark green color still present in most of the piece, the authors suggest that this is due to the presence of iron. Until about the middle of the 2nd century AD, Roman glass was made from crude Levantine Syrian glass made from relatively clean sand, producing a black/purple color, or from high-magnesium glass made from impure sand rich in iron and toppings. of plant ash to give them a dark green color. This is consistent with this new “blinding glass” analysis.
Zoom in / Highly regular, nanometer-thick layers of silica form a mineral patina on a piece of Roman glass.
Silklab, Tufts University
SEM analysis revealed a precise hierarchical arrangement, forming so-called ‘Bragg stacks’ – essentially one-dimensional photonic crystals characterized by alternating layers of high- and low-refractive-index materials that produce structural color. In an ideal Bragg stack, the layers are of equal thickness. But one layer was thicker and denser than the other in the ‘dazzling glass’, giving it a cool metallic look. Specifically, each stack of screws reflected a different narrow wavelength of light, and stacking dozens of screws together created a highly reflective layer of gold on top of the case.
This is evidence that the glass fragment was created through a “pH-induced chemical change in silica that does not impose the same strict physical constraints as in natural animal systems,” the researchers write. In accordance with to Ominito, If they can figure out a way to speed up this process so that it doesn’t take centuries to create such an artifact, “we could find a way to grow optical materials instead of manufacturing them.”
“It’s probably a process of erosion and renewal.” said co-author Giulia Guidetti, also at Tufts. “The surrounding clay and rain have determined the diffusion of minerals and periodic erosion of the silica in the glass. At the same time, 100-nanometer-thick layers that combine silicon dioxide and minerals in cycles have also been collected. The result is an incredibly ordered arrangement of hundreds of layers of crystalline material. Crystals growing on the surface.
PNAS, 2023. DOI: 10.1073/pnas.2311583120 (About digital IDs).
2023-09-18 21:20:32
#Ancient #Roman #dazzling #glass #photonic #crystal #tiara #built #centuries #Ars #Technica
