Red Dwarfs, Nanoparticles and the Colors of Glass: Guest Post by Michelle Francl-Donnay of Quantum Theology

Today I am sharing blog space with Michelle Francl-Donnay.  Michelle found Stratoz’s blog, because she too was going to Wernersville Jesuit Center for a silent retreat.   I met Michelle  in 2008, when she came to one of our craft shows. She wanted to meet us, and ended up smitten with my Spiral Mandala, and purchased it for her prayer space.  She is a delightful combination of Ignatian spirituality, thoughtful writing, and Professor of Chemistry. Be sure to check her out at Quantum Theology, and see the pure awesomeness of her photo mosaic of Marie Curie, composed of 270 female scientists.


Gold nanoparticles, from Wikimedia and used under a Creative Commons license.

 

Red Dwarfs

I want to thank Margaret for her invitation to visit her blog and talk
about chemistry and color. I have a gorgeous mosaic by Margaret
hanging on my wall — deep blues and golds spiraling inward. I
love Margaret’s art, but I also enjoy her poetry. She’s writing about
Marie Curie, in poetry and prose over at my blog today. Do come
visit Marie and Margaret there!

If you see a colored compound in chemistry, you can almost bet that it
will contain a transition metal. Though we think of metals as being a
shiny grey hue (with a few exceptions, gold being one), metals are key
to color, particulary in art. The visible frequencies of light are
relatively low in energy, and correspond to the small gaps in energy
that electrons can leap in metals (what chemists call d to d
transitions). Cobalt blue, one of my favorite hues, is (as its name
suggests) a cobalt salt: CoAl2O4.

To get different colors, you have to use different metal salts. You can get
a brilliant yellow using lead chromate, the same chrome
yellow that Vincent Van Gogh used
. Tweaking colors to get
slightly different hues requires either mixing materials or finding a
different salt altogether, the gaps that the electrons leap over when
they absorb light aren’t adjustable.

But there are other ways to create color using metals. Red stained
glass has been made for centuries by adding gold to molten glass and
carefully controlling the temperature. The gold clusters together in
small particles which then become evenly distributed and suspended in
the glass.

These tiny clusters are called nanoparticles, because they are 100
nanometers or less in size. One nanometer is 1 billionth of a meter,
the period in this sentence is about a million nanometers across, the
little gold balls in red glass are about 25 nanometers in diameter.
The prefix nano, comes from the Greek word for “dwarf,” hence the
title of this post. Nanoscience is older than you think!

The gold nanoparticles are not dissolved in the glass, but form a
colloid. And one property of colloids is that they scatter light.
Different frequencies of light scatter differently, which is why the
sky is blue, though the scattering of light by a colloid is a slightly
different process. (Scattering isn’t the only process involved in the
color, but unless you really want to fly off the math cliff with me,
let’s leave talk of quantum dots and wavefunctions to another day.)

The color of light that a colloid scatters depends on the size and
shapes of the particles dispersed. It turns out just by varying the
size and shape of the particles involved you can tune your gold
nanoparticles to be red, red-violet or even green and many colors in
between!

If you are interested in knowing more about the history and chemistry
of color, Bright Earth: Art and the Invention of Color by Philip
Ball is a terrific introduction. For a readable introduction to
nanoparticles, quantum dots and color, try this
article
in the NY Times.


The
photo
is from Wikimedia and used under a Creative Commons license.


More Marie:
X is for X-Ray and Marie Curie’s Quest to Help the Wounded in WWI

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  1. Science and glass!