The mysterious Roman cup that changes color.

In the 1950s the British Museum purchased an ancient glass chalice called the Lycurgus Cup, named after its description of the triumph of Dionysus over King Lycurgus of Thrace, which is entangled in grape vines on the outer surface of the cup. The craftsmanship is excellent, the interior is smooth while the exterior has been meticulously carved and etched to create a decorative cage-shaped structure around the inner canopy. This type of Roman vessels are known as cage vessels, and were mostly made during the fourth century BC Some fifty or so cups have come down to us from various archaeological excavations , mostly in fragments, but only a few almost Complete. The Licurgo Cup is one of these best-preserved Roman vessels.

These cups were extremely difficult to make and certainly very expensive, but this particular specimen is distinguished because it shows a strange optical phenomenon that had perplexed the experts for decades. Under normal lighting conditions, the glass looks jade green, but when illuminated from behind, it becomes ruby ​​red. Initially, experts were not sure whether the glass was glass or was a gemstone. It was not until 1990 when researchers discovered how these strange color changes worked.

It appears that the glass contains minute quantities of gold and silver particles that have been ground so finely that their diameter is only 50 manometers, or less than a thousandth the size of a grain of salt. The amounts involved are so small (330 parts per million silver and 40 parts per million gold) that the researchers speculate that the glass could have been accidentally contaminated with gold and silver dust and that glass manufacturers would not even have Account of this contamination. However, the discovery of other pieces of glass with the same proportion of said metals in their composition demonstrates that the glass was so deliberately fabricated. Somehow, ancient Roman glassmakers realized that when light strikes the glass embedded with the smaller particles of gold and silver, the color of the glass is altered. Modern science has a name for this effect, dichroism, and the glass that presents this phenomenon is known as dichroic glass.

But this is not the end of the story. The simple addition of gold and silver to the glass would not produce these unique optical properties. In order to produce the phenomenon described above, it is necessary that the gold and silver particles form submicroscopic or colloidal crystals. It is these colloids that give rise to the dispersion of light that results in dichroic effects.

The addition of metals or metal oxides to color glass was not unknown for Roman glassmakers. For example, red and brown opaque glasses were made by the addition of copper. However, coloring glass using gold and silver was far from routine and complicated. In the process, a large number of factors were involved that had to be perfectly controlled, such as metal concentration and particle size, oxidation states of certain elements, cooking time and temperature and probably the Atmosphere during baking. It is unlikely that the Romans were able to understand the whole process, especially considering that it occurred 1,600 years ago, when the technology was very restricted.The inability to control the coloring process explains why this technology never developed beyond the fourth century after Christ. The Licurgo Cup is an exceptional example and is one of the most sophisticated glassware ever made before the modern era.

There are other examples of the use of nanotechnology in ancient history. The Mayan people produced a corrosion resistant blue pigment known as Maya Blue resistant to light, bio-corrosion and moderate heat, does not discolour against concentrated nitric acid, alkalis or organic solvents, and the murals executed with it Have tolerated moisture well for hundreds of years. The steel swords of Damascus, a steel with a very high carbon content, in a purity and resistance unknown at the time. These swords were produced in the Middle East between the third and seventeenth centuries.

The presence of nanoparticles in these materials, however, does not mean that ancient peoples knew anything about nanotechnology.

Ian Freestone, of the Institute of Archeology at the University College London, who studied the glass of Lycurgus, believes that these ancient craftsmen “were very skilled but they were not experts in nanotechnology.”“They did not know they were working at the nanoscale.”

 

 

 

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The mysterious Roman cup that changes color.

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