Saturday, March 01, 2008

Cookies, Palygorskite, and Maya Blue

A Maya mural paining, on a background of Maya Blue (Source: Wikipedia, and azulmaya.com).
On Thursday the New York Times science news feed linked me to "The Grim Story of Maya Blue". Maya Blue is a bright blue colour that had been used by the Maya people of Central America to paint murals, pottery and artefacts, and for ritual purposes. It's a very persistent pigment that remains even after all others dyes have faded. The New York Times article reports new insights how this pigment actually was produced by the ancient Maya. The frisson of humans painted in Maya Blue before being sacrificed to the Rain God Chaak notwithstanding, I just had a short glance at the article when I was stuck by the mentioning of the mineral used to make the pigment, palygorskite. What a surprise!

Like probably most of you, I guess I never would have heard of palygorskite before, had I not been dealing with a long manuscript about the structure and properties of just this mineral earlier this week. There can be funny coincidences...

Palygorskite, or attapulgite, as it has also been called, is a clay mineral, belonging to a large group of clays known as Fuller's Earth. Technically speaking, it's a magnesium aluminium phyllosilicate with the formula (Mg,Al)2Si4O10(OH)·4(H2O).

This formula looks very complicated, but actually, silicate minerals are quite fascinating stuff. Essentially they are built up of small tetrahedra of silicon atoms surrounded by four oxygen atoms, and octahedra of metal atoms (magnesium and aluminium, in this case) in the centre of six oxygen atoms. Like building bricks from a kid's construction kit, these tetrahedra and octahedra can be combined in a huge number of regular patters, giving rise to the enormous botany of different silicate minerals. In phyllosilicates, the silicon tetrahedra and metal octahedra form planar sheets (hence the name), which then build up layered structures.

Palygorskite has such a layered structure, but actually, it is very uncongested. It does not consist of continuous sheets, but of long bars of layers of metal octahedra sandwiched between silicate tetrahedra. These bars, then, are arranged parallel to each other in a kind of checkerboard pattern, with large, channel-like empty spaces in between.



In this cookie model, the chocolate filling represents the metal octahedra, which are sandwiched between the biscuit, standing for the silicate tetrahedra. You see a cross section through the parallel arrangement of long bars. A more technical illustration is shown in figure below, which has been adapted from the paper On the unusual stability of Maya blue paint: Molecular dynamics simulations, by Ettore Fois, Aldo Gamba, and Antonio Tilocca, Microporous and Mesoporous Materials 57 (2003) 263-272:



The cross section through the basic building bar is marked by the grey rectangle. This basic building block is repeated in a checkerboard pattern in the plane of the figure, and just continues along the axis normal to the figure plane. You can see the silicate tetrahedra, with oxygen atoms at the vertices, and the metal atoms - the large dark-grey spheres surrounded by six oxygen atoms each.

The empty, tunnel-like spaces between the bars are not completely empty, however. Usually they are filled with water molecules. A few of these molecules can be spotted in the illustration above. But if other molecules are around, they can enter the tunnels, and physically bind very efficiently to the silicate framework. For this reason, palygorskite has often been used in medicine: The mineral is not absorbed by the body, but binds acids and toxic substances in the stomach and digestive tract. Thus, it acts as an antidiarrheal medication, for example.

The same thing happens when palygorskite is brought together with Indigo, a dye that can be be extracted, for example, from a plant named Añil, which is native to tropical America.



Indigo molecules fill the channels of the palygorskite structure in a random pattern, as shown in the illustration, which has also been taken from the paper of Ettore Fois, Aldo Gamba, and Antonio Tilocca. The silicate hull shelters the dye molecules, and thus creates the enormous persistence of the pigment and its robustness against harsh climatic conditions, alkali and acid treatment and organic solvents.

How to create this indigo-clay pigment is what the ancient Maya had discovered - that's Maya Blue.







  • Mineralogical details about palygorskite can be found at the databases mindat.org
    and webmineral.com. Webmineral.com has also a very nice JavaApplet to explore interactively the unit cell of palygorskite.

  • The peculiar crystal structure of the palygorskite mineral was described for the first time in The structural scheme of attapulgite by W. F. Bradley, American Mineralogist 25 (1940) 405. Bradley used the classical x-ray diffraction technique, and you can have a look at the PDF file of the paper.

  • Since the 1940s, mineralogists have applied the whole arsenal of methods provided by modern condensed matter physics to shed light on the structure of palygorskite and its role in the properties of Maya Blue. A very recent review is Pre-columbian nanotechnology: reconciling the mysteries of the maya blue pigment by G. Chiari, R. Giustetto, J. Druzik, E. Doehne and G. Ricchiardi, Applied Physics A: Materials Science & Processing 90 (2008) 3-7 (subscription required).

  • For more about the archaeological aspects of Maya Blue, see the entry The Palygorskite and Indigo Mix of Maya Blue at about.com:archaeology as a starting point.



13 comments:

Phil Warnell said...

Hi Stefan,

A very interesting article and one that indicates your curiosity and knowledge are just not restricted to just physics. Your description of palygorskite’s structure and function reminds me somewhat of fullerenes or what is commonly known as “Bucky balls”. Besides being the largest known carbon molecule (60 atoms) it also has the potential to form a cage around other substances. However, I believe that it leaves the contents opaque in terms of viewing where as palygorskite is transparent in terms of its content. It also suggests that it just wouldn’t contain and preserve only indigo as a pigment yet other colours as well. Do you know if this has been exploited by any current day producer of paints or pigment?

The Maya connection I’m also interested in and familiar with, as this extinct civilization has always fascinated me from more then one perspective. I visited Chichen Itza and looked into Sacred Cenote (sacred pool) and was told the related story. Also, in my office behind my desk I have a photo I took there , had enlarged and mounted taken of the wall next to the Ball yard. The people depicted wear costumes, hold and carry items that make one wonder and speculate what they may be. Also, they all hold their hands in a configuration where all the fingers and thumbs are extended except the middle two which are curled in to form what appears like bull’s horns. I have always wondered what this was to mean. The Maya were also of great interest to Richard Feynman who actually helped in deciphering the language. So yes I find lots within this post that fascinates me and thank you for it.

Best,

Phil

Odysseus said...

Great post! As an ancient history teacher, I am fascinated with Maya culture. I had the opportunity to explore Chichen Itza a few years back. What an amazing place!

I recently wrote a post about the movie Apocalypto and its mythic depiction of the Hero's Journey. I'd love to hear your thoughts on the post if you have a moment.

http://eteaching101.blogspot.com/search/label/Apocalypto

stefan said...

Hi Phil, Jay:

actually, I do not know very much about the Maya, and I've never been to Central America to see their remains. And I have to say I did not intend to read the NYT article, I had just klicked on it and very briefly skimmed over it, when I got stuck by this strange word, "palygorskite"... it was really a funny coincidence.

But then, I was quite fascinated to see how modern, sophisticated materials science methods can help to understand the special features of this pigment.

Jay, I didn't see Apocalypto, and I am not sure if I am actually missing it... But thanks for you comment, it's an interesting aspect! BTW, can you say something about "10.000 B.C."? I am not sure if has already been released in the US. There seem to be similarities in the plot, at least, the hero kidnapped by a kind of "advanced" civilisation?

And I like your post about the Starbucks logo :-)


Best, Stefan

Odysseus said...

Hi Stefan,

You'll have to visit Chichen Itza sometime. The sense of being in the presence of a powerful history is overwhelming.

About 10,000 B.C., the movie, I've only ever watched the previews...but it seems to play fast and loose with what we know of the past. Twelve thousand years ago, there was no advanced civilization. Civilization emerged in the Fertile Crescent approximately five thousand years ago (3000 B.C.). Prior to that there were Neolithic farming settlements, but no real cities to speak of.

Being an action buff, I'd still like to see it. I maintain a site for my ancient history course. It's entitled Adventures in World History. You may find it a little middle schoolish, but then again, I am a seventh grade teacher. :)

http://www2.svsd.net/~lions/world.html

Keep up the good blogging!

Jay

paul valletta said...

Hi Stefan, from the model of biscuits and sweets, you have created a carbon-copy of http://en.wikipedia.org/wiki/Image:Chichen-Itza-Castillo-Seen-From-East.JPG

except for the steps! great and very interesting culture, best to you both paul.

a quantum diaries survivor said...

Hello Bee/Stefan,

I took the liberty to tag you for one of those internet memes... See here...

Cheers,
T.

Plato said...

Hi Stefan,

Since you had tagged it useless knowledge it reminded me of your post on carbon. Thought you might like to add Red Ochre as well.:)

Red ochre and yellow ochre (pronounced /'əʊk.ə/, from the Greek ὄχρος, yellow) are pigments made from naturally tinted clay. It has been used worldwide since prehistoric times. Chemically, it is hydrated iron (III) oxide.

Ochres are non-toxic, and can be used to make an oil paint that dries quickly and covers surfaces thoroughly. Many people believe that the best ochre comes from the area of Roussillon, France.

To manufacture ground ochre, ochre clay is first mined from the ground. It is then washed in order to separate sand from ochre, which can be done by hand. The remaining ochre is then dried in the sun and sometimes burned to enhance the natural colour.

Phil Warnell said...

Hi Stefan,

I would agree with Jay that Chichen Itza is one place that won’t disappoint if you were to ever visit. I was there for one full day as part of a weeks vacation to Cancun (back in the late 80’s) and after wished I’d spent the week there. When Jay says “the sense of being in the presence of a powerful history is overwhelming”, it’s an understatement. From the way he’s put it, I think his impression was more like mine, in that I found it down right spooky and I don’t believe in spooks. It comes from the fact that much of the site is still intact and you are not just impressed by the pyramid yet also the observatory, ball yard and many other structures, glyphs, carvings and paintings.

However, most of all you truly feel like you’re in a ghost town (city), wondering were all the inhabitance went. It’s also a bit of a reality check for us westerner’s who come to believe that civilization has only one main branch. Also, it serves to in part dispel the popular myth, that it was only the west that was responsible for all the cultural upheaval in the new world. The Mayan civilization had totally collapsed more then a century before Columbus made his journey. The Spanish would find Chichen Itza overgrown and hidden by the jungle. It makes one wonder if there will ever be a time in the future when our civilization will be viewed from such a perspective.

Best,

Phil

amaragraps said...

Dear Stefan, What a great post! And your cookie photos made me hungry. Here are some sweets to return the favor!

Plato said...

Phil:When Jay says “the sense of being in the presence of a powerful history is overwhelming”, it’s an understatement. From the way he’s put it, I think his impression was more like mine, in that I found it down right spooky and I don’t believe in spooks.

As mysterious as it may sound, "geometrical presence" was never considered either, and to think Plato and his forms would actually exist in some place not considered is equally valid from the point of "awareness in science."

So to me "spooky" was definition given to something happening in science that while mysterious, directed our views with regards to science and it's undertakings. We know it's history with Einstein do we not?

You pointed out the "memories of things" that are labelled as spooky, but I would contend that the memory of things is as much a vital link to the manifestation of materials as to record along with it, it's time. Sure polarization within it? Still talking about something else.

Looking at Einstein's quote is often revealing.

A knowledge of the existence of something we cannot penetrate, of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms—it is this knowledge and this emotion that constitute the truly religious attitude; in this sense, and in this alone, I am a deeply religious man.

Einstein, Albert (1949). The World as I See It. Philosophical Library. ISBN 0806527900.

The "feeling of the mysterious" may come off vague within our perceptions of things, and we try to classify it within our own reasons. So to me it is more then just calling it spooky. Requires a deeper in take of the things that may move through one's mind at the time. Getting intune. Unfortunately we create the movies, yet, it would have been nice to switch a dial and actually look at the history unfold.

Would it not be nice to have such a device?:) Sorry Stefan, more useless knowledge

stefan said...

Hi Paul,

It didn't occur to me at all that I have built a small Mayan pyramid with the cookies ;-), thanks, that's a nice coincidence.

BTW, Amara, I had to cut quite a lot of the cookies until I had figured out how to do this without breaking them, so that I did end up with my model silicate layer slabs. Of course I had to eat all the failed slabs, and you can imagine that for the time being l have enough of them ;-)


Best, Stefan

Georg said...

Hello Stefan,
here is some not so ancient song on
"woad" (same as German "waid") the
indigo painting of the ancient britons:
----------------------------------
Tune "Men of Harlech":

The Song of the Ancient Britons

What's the use of wearing braces
Socks and pants and shoes with laces
Other things you buy in places
Down in Saville Row.
What's the use of shirts of cotton,
Studs that always get forgotten,
Such affairs are simply rotten
Better far is woad.

Woad's the stuff to show men
Woad to scare your foemen
Boil it to a brilliant hue
Then rub it on your back and your abdomen
March up Snowdon with your woad on
Never mind if you get rained or snowed on
Never want a button sewed on-
Tailors, you be blowed.

Romans came across the channel
All dressed up in tin and flannel
Half a pint of woad per man'll
Dress us more than these.
Saxons you may waste your stitches
Building beds for bugs in breeches
We have woad to clothe us which is-
Not a nest for fleas.

Romans keep your armours
Saxons your pyjamas
Hairy coats were meant for goats
Gorillas yaks retriever dogs and llamas,
Ancient Briton never hit on
Anything as good as woad to fit on
Necks or knees or where you sit on-
-----------------------------------
So, is there some relation between Britons and the Maya? Fled some Britons
after Boudiccas defeat cross the ocean??? :=)
To be serious, it is possible to
sublimate Indigo, it is done as final purification step in production of the dye.
If those mayas made the pigment
from indigo and the silikate by heating
in a pot, they should have mixed the
silikate and the indigo as perfect as possible, rather likely the resin
was used to cover the mixture to exclude
oxygen.
Georg

Anonymous said...

Hi Stefan,
being strictly interested in the scientific study of this pigment,
I just wanted to tell you that your "Cookie Maya Blue" model is absolutely wonderful!
Best greetings.
Roberto