#1 By: Maggie Koerth-Baker, August 30th, 2013 13:28
#2 By: Edwin Gore, August 30th, 2013 14:03
Immediately makes me think about the legendary use of amethyst to detect poisons - I wonder if there is any connection? That would be a pretty sweet ancient grift to run.
#3 By: Noah Django Gross, August 30th, 2013 14:05
everything about this is cool. the science angle is probably the the most cool and improbable aspect of the story, closely followed by the fact that the extraordinarily fragile object survived the fall of Rome etc, closely followed by the stunning beauty and craftsmanship of the object. synergy!
#4 By: Douglas Stuart, August 30th, 2013 14:43
The mystery wasn’t solved until 1990
Old news is old. But still interesting!
It would most likely NOT change color in the presence of water, or poison. However, the same physical phenomenon (localized surface plasmon resonance) CAN be used for ultra-sensitive detection. See here:
The actual synthesis of gold and silver colloids is quite easy, and I have my undergrads do it in chem lab. See here:
#5 By: Daemonworks, August 30th, 2013 15:51
Maggie... They changed colours based on the direction of the light source, not the contents of the cup.
#6 By: Mellivora Capensis, August 30th, 2013 15:55
The Lycurgus Cup is a 1,600-year-old glass chalice
I was going to ask what this had to do with Ancient Romans, but Wikipedia tells me the definition of antiquity is pretty loose.
#7 By: Mellivora Capensis, August 30th, 2013 15:55
Since the museum probably wouldn’t like you pouring your cereal in the
goblet, the researchers instead re-created the cup’s material on a
chip. When they poured solutions of water, oil, sugar and salt onto
the surface the colors indeed changed markedly—light green for water
and red for oil, for instance—according to research published earlier
#8 By: Maggie Koerth-Baker, August 30th, 2013 16:23
The tests they've run on similar material suggest that it would, actually, change color depending on what you put in it. It's there in the story.
#9 By: Tristan, August 31st, 2013 00:59
I work in this field. The paper cited by Discover Magazine, Gartia et al., is very misleading.
The glass in the Lycurgus cup contains metal nanoparticles distributed throughout it. These reflect green light and so the cup looks green in reflection. They absorb or scatter blue and green light, so the cup looks red when light is shone through it.
Gartia et al have made a structure that contains metal nanoparticles, but the fabrication method, the type of nanoparticles and the way the nanoparticles are positioned and structured, are all completely different to the Lycurgus Cup. They claim the association simply because their structures also look green in reflection and red in transmission. Many, many structures share the sample optical properties: it's not called "the Lycurgus Cup effect", it's called dichroism.
The structures made by Gartia et al are very thin films of gold perforated by tiny cone-shaped holes, which are filled with nanoparticles. The cones and the nanoparticles are exposed to the external environment, and so come into contact with whatever liquids you put on them. The liquids change the optical properties of the metal nanoparticles because they change the local refractive index (and hence the effective wavelength of incident light) which changes the apparent colour. This is a very well known effect, and makes metal nanoparticle extremely useful as optical sensors. However it's not the reason for the colouration of the Lycurgus Cup.
In the Lycurgus cup the nanoparticles are deeply embedded into the glass. There's no sheet of gold, and no tiny cones, just a whole bunch of nanoparticles randomly distributed throughout the glass. The optical properties of the nanoparticles are only sensitive to the material immediately surrounding them (i.e. the material within about 20-30 nanometres of the particle surface). Liquid poured into the cup does not come into contact with the metal nanoparticles, and so does not affect their optical properties.
The rest of the Gartia et al's paper actually looks quite interesting, but it has very, very little to do with the Lycurgus cup. I'm sure the authors know this, but "dichroic plasmonic sensing" doesn't sound as sexy as "ANCIENT ROMAN SENSING TECHNOLOGY!!!"
#10 By: Tennessee Waltz, August 31st, 2013 14:40
I was going too say that too. Silver and gold... solar metallurgist must have had a nice Guild back then.
#11 By: Yama Ploskonka, September 1st, 2013 00:52
Sad. People learning technology in a buzz-word infected time.
My dad taught me about "Cassius red" when I was 10 or so - we actually do have a cup made in Czechoslovakia using this technology -WAAAAY before such content-free word as "nanotechnology" was popular. (turns out it's supposed to be "Cassius Purple", same difference). See "Pigment Compendium" by Walsh/Chaplin for details, Google Books has this page available
The Discover article is rather worse on what Tristan indicates was a poor paper to begin with. Sorry I sound so negative. As a word/concept, "nanotechnology" is fancy, but out of reach "obey the scientists, we will take care of you".
"fine precipitate" is something I could understand at that young age, and felt quite capable to emulate if I cared, or at least try, "I can take care of myself just fine".
One choice of words empowers Makers, citizen-scientists, people that participate. The other type of copy enforces the separation between the Experts and the sheeple. Discover, ahem, what side is it on?
#12 By: Tristan, September 1st, 2013 02:03
Purple of Cassius is a suspension of gold nanoparticles in liquid. The red (or purple) colour arises because the nanoparticles absorb blue and green light, but do not strongly interact with red light. So this is a form of subtractive colouration, just like all pigments and dyes. Adding Purple of Cassius to molten glass results in a red colouration because the nanoparticles become distributed throughout the glass. This is how ruby glass (or cranberry glass) was made from the 17th century onward, and was also used prior to this in stained-glass windows etc.
However, ruby glass and Purple of Cassius are the same colour if you shine light through them or reflect light off them, it's red in both cases. The Lycurgus Cup is different, and the difference is due to the size of the particles. Particularly tiny gold nanoparticles (with sizes less than a few tens of nanometres) only absorb light, so they act like a pigment. However the particles in the Lycurgus Cup are quite a bit bigger than in Purple of Cassius, around 50-100nm in size, so they also scatter light. The red colour in transmission is due to absorption, just as it is in ruby glass and Purple of Cassius. However the green colour is due to scattering of light, which you only get when the particles are big enough.
It's this dependence on size that I think justifies the use of the word "nanotechnology" for the Lycurgus Cup and for Purple of Cassius. I use the word when I'm referring to a technology that utilizes feature sizes less than 100 nanometres, and -crucially- that gains unique properties by being this size. The colour of gold nanoparticles is extremely sensitive to their size and shape, and it's only when they're "nano sized" that you get such beautiful effects.
I feel like I'm writing to an increasingly diminishing audience, but hopefully someone finds it interesting...
#13 By: Maggie Koerth-Baker, September 4th, 2013 13:28
This topic was automatically closed after 5 days. New replies are no longer allowed.