Page 4 - ScienceFocus (Issue 014)

STAINED GL ASS

敶抵?餌?

?tained glass.??What word comes to mind when you hear this?

Common answers may be ?rt??or ?athedral.??Surprisingly, ?anotechnology??is
also a correct answer. Though the ancients did not realize it, they created art with one of
today? most researched branches of science. Stretching as far back as the dawn of human
civilization, the history of stained glass is one rich in art and science. In fact, it could be said
that the art of making stained glass was the first work of nanotechnology and its craftsmen
the very first nanotechnologists.

To appreciate this amazing story of how science and art intertwined, here? a brief history
of stained glass. Historical records show that the earliest stained glass works were created
in Ancient Egypt and Ancient Rome. They gained popularity in the Middle Ages. In the 12th
century, the development of stained glass windows reached its height. The rise of stained glass
at the time owed much to both the rise of Christianity and the Gothic style of architecture. This
architectural design made it possible to increase the amount of glass paneling in a building.
Instead of thick stone walls, Gothic churches had large openings in walls decorated with stained
glass windows prominently displayed as works of art and a means to educate people of their
religion.

One of the more famous examples of all time resides in the Chartres Cathedral in France.
Constructed from 1194 until 1220, a grand total of 176 pieces of stained glass were installed in the
cathedral, the most famous being the ?otre-Dame de la Belle-Verri癡re.??It contains 24 segments
showing scenes from the life of Christ. At the center of the window, there is a figure of the Blessed
Virgin Mary on a throne with the Christ Child on her lap. Comprised of a myriad of red, blue and green,
the window is a breathtaking sight to behold. Imagine standing in the soaring cathedral, gazing up at
the play of light on the rich colors. The powerful images may make you wonder: What was the secret
discovered by Medieval craftsmen? How did they create such awe-inspiring art work which shimmers in
multiple colors?

Here? the science behind stained glass. It is not as complicated as you might imagine. Regular glass is
produced by heating silica to a very high temperature. Stained glass is made from pretty much the same
process, except that traces of metal oxides or metals are added to the silica when it is still molten. This very
slight amount of metal makes a huge difference ??a spectrum of colors is produced. The secret lies in the
fact that the traces of metal trapped in the glass matrix are the size of nanoparticles. On the surface of metal
nanoparticles there are loosely held electrons, and as light shines through the glass, these electrons interact
with energy-carrying light waves and begin to oscillate. The oscillation at once absorbs and reflects light of
specific wavelengths. A glass matrix containing spherical gold nanoparticles of 25 nanometers (i.e. 10-9 m) will
appear ruby red to the eye because shorter wavelengths in the blue color range from visible light are being
absorbed while longer wavelengths in the red color range are being reflected into your eyes. Slight variations in
size of the nanoparticles will change the frequency of the oscillation, affecting the wavelengths of light being
absorbed and reflected, consequently producing the different colors we see.

A rule of thumb is that when the size of the nanoparticles increases, the wavelengths they absorb are also
increased, while the wavelengths they reflect are decreased. So if the size of the gold nanoparticles trapped
within the glass matrix are bigger, they will absorb longer wavelengths of red colors and reflect the shorter
wavelengths of a vivid blue color instead. To produce a wide array of colors on a piece of glass, gold, silver or
other metal/metal oxide nanoparticles of different sizes can be trapped into glass matrices according to specific
structures. Simply put, it all comes down to one thing when we talk about the kaleidoscope of colors in stained
glass windows: size!

So there you have it. History, art and science all rolled into one fascinating story. Behind the beauty of art lies
the art of science. Their combined creation bore witness to the history of men?
attempts at creating beauty. Whoever thought all three
would be so interconnected? Well, now
you know.