Friday, March 28, 2008

Blue rose

Suntory Ltd. blue roseOn next year's Valentine Day your roses might be blue. Suntory Ltd. has obtained government permission to market the world's first blue rose that it developed in 2004. The company plans to put it on sale in 2009 after building production facilities and sales outlets.

Roses have no genes to create a blue pigment, and rose growers have long worked hard in vain to produce a blue rose. In English, blue rose is a synonym for impossible. Suntory organized a Blue Rose Development Team jointly with its Australian subsidiary in 1990 and successfully produced a blue rose by recombining a gene capable of creating a blue pigment taken from pansy, using gene-splicing technology. In the process of the research, the team has succeeded in developing a blue carnation, which is already on sale in Japan.

A blue-like rose has already been produced by suppressing a red pigment through cross breeding and marketed in the world. But no rose with a blue pigment has ever been marketed yet.

Source: Kansai Window, Kippo News, Vol.14 No.562, Wednesday, February 20, 2008.

Wednesday, March 26, 2008

Performance update

A year ago I posted two entries on hyperthreads and multicores that were relatively popular. A short post on the the Performance Agora has an interesting comparison of the performance of the latest crop of Intel chips suggesting that the 8-way Penryn TPC-C performance now matches a 16-way Xeon of 2 years ago.

Performance experts like Neil Gunther worry mostly about database transactions and servicing HTTPS requests. For us color scientists working on color reproduction systems, the performance picture is different. Historically, we have always been fighting with the problem that we are ten years behind marking engine designers in terms of ripping pages as fast as the printers can consume them.

For us the hour of truth will come at the end of this year, when Intel will start shipping Nehalem. We will have to revisit our software architectures to take advantage of the new QuickPath platform architecture with fast integrated memory controllers. With QuickPath each processor has its own dedicated memory, so we will have to redesign how we map rendering in memory.

Faster bus and better stall prevention, will probably allow us to use more GPUs per system, which will likely require we rearchitect our whole rendering pipelines.

For more details on Nehalem, see Intel's whitepaper. For more details on QuickPath, see this other withepaper.

Tuesday, March 25, 2008

IS&T fellows

On behalf of the 2008 IS&T Honors and Awards Committee, the Society for Imaging Science and Technology (IS&T) today has announced those individuals selected for 2008 IS&T Fellowship. Fellowship is awarded to a Regular Member for outstanding achievement in imaging science or engineering. Ordinarily this will be demonstrated by citing several journal publications or patents for which the candidate is the sole or major contributor. Regular membership in the Society for at least three years prior to the time of nomination is required. At the time of award, the recipient must be a Regular Member in good standing. Not more than five awards per year are bestowed.

The new IS&T Fellows are:

  • Roger David Hersch (Ecole Polytechnique Fédérale de Lausanne) “for his contributions to halftoning, multispectral imaging, and digital typography”
  • Nathan M. Moroney (Hewlett-Packard Company) “for his contributions to scientific experimentation, practical application, and standardization of innovative color imaging technologies”
  • Richard Veregin (Xerox Research Centre of Canada) “for his contributions to electrophotographic toner and developer design”
  • David S. Weiss (Eastman Kodak Company) “for his contributions to the science and technology of electrophotographic imaging materials”

I am proud I can count the first half as longtime friends.

Roger David HerschRoger was a year ahead of me studying mathematics at the Swiss Federal Institute of Technology (ETH) in Zurich. We got to know each other by being both active in the Filmstelle, a student organization that twice a week borrowed cinematographic masterpieces from the Cinémathèque Suisse in Lausanne and exhibited them in a large auditorium.

Nathan M. MoroneyNathan (here with his wife Elizabeth Pirrotta) goes back to when I was taking courses in color science from Robert Hunt and Mark Fairchild at the RIT Munsell Color Science Laboratory and he was a student there. We both ended up at HP Labs and as you know we are partners in crime by conspiring to write this blog for you.

Research policy update

From time to time I have been posting about the research process itself, i.e., research policy. Today I will just post two links to two other blogs with recent posts on this subject.

Jon Stokes writes on ars technica on paying for secrets: national security versus tech innovation, while Neil Gunther writes on Performance Agora on USA High Tech R&D Trending Down.

Saturday, March 22, 2008

This is not Easter Blue

Easter Blue

In a recent paper with Silvia Zuffi and Carla Brambilla on color readibility, we wrote that you can perform psychophysics on the Web even if it is uncontrolled, because the errors average out and you can recruit a large crowd of observers. Sure, Carla had to prune some non-sense outliers, but statisticians know how to do that correctly.

On the other hand, the Germans have the saying "even if a gazillion flies eat shit, this does not mean that shit tastes good." In the color readability test, the task was sufficiently arcane that we can safely assume that the subjects had some domain knowledge and knew what they were doing. But what if the task is so easy and natural that anybody can perform it. Do errors average out when you do a viral Web experiment? Let us find out!

Now that it is Easter, you can go to Nathan's post on his On-Line Color Thesaurus and enter Easter egg blue. His tool will return color #66CCEE shown above. Hmmm. Where does that color come from? No, he did not make up the name. What he did was to use the Internet and his Color Naming Experiment to have a crowd come up with that name. He showed them a patch of #66CCEE and got back Easter egg blue.

How authoritative is this datum? We can search Easter egg blue on the Internet and we get 8,050 hits. A relatively low number, and not a clue on the name's history. We get a better datum by checking the raw data on the server; the number of people who proposed that name where only three. Hardly an authoritative number.

For privacy reasons we do not collect any demographic data from the Web site, so we cannot go back and ask these three people how they came up with the name; we have to come up with a plausible argument.

Easter is not blue. Here in the USA we have the concept of holiday blues, but it refers to the time from Thanksgivings to Christmas. And what do eggs have to do with it? Is it blue eggs then? Indeed, when you tried the query on the on-line color thesaurus you got robin egg blue as a synonym. But when you click on it, you are told it is color #55CCE5. Here are the two color side by side

Easter Blue vs. Robin Egg Blue

They are pretty close, but do not match. The Wikipedia thinks Robin egg blue is color #00CCCC, but they do not give a source.

Egg Blues

by Dmytro SergiyenkoA different approach is needed. Human memory is not cast in concrete, it has to be continuously refreshed by reliving memories. When a human is isolated, his memories are not checked and it drifts. And because memory is associative, we can easily get side-tracked by incorrect associations.

It is possible, that our famous three subjects had at some point heard Easter Blue, but because it does not make sense in isolation, they somehow added egg. Indeed, The ISCC-NBS Color Name Dictionary lists an Easter Egg Yellow, but no Easter Egg Blue. My wild guess is that the three subjects were thinking turquoise.

Turquoise is a strong hint. The next stong hint is: it is not a solid color at all.

Blue and green cabochons showing spiderweb, Bunker Hill Mine, Royston

If you cross the Death Valley from west to east and after enjoying the famous opera at Amargosa Valley drive north on Highway 95, on your right you will drive along the Tonopah Test Range, and finally hit Tonopah. In Tonopah you will find the Easter Blue Mine owned and operated by Danny and Dean Otteson. You can see the very approximate location on this map, and here is information on Nevada Turquoise.

A Web site on the New Nevada Turquoise Trail has a page on Easter Blue, depicting a number of Easter Blue stones you may want to check out. They explain: "The Easter Blue mine is located northwest of Tonopah, Nevada a few miles from the Royston district. Turquoise from this claim has also been called Blue Mountain and Blue Gem. Compared to some of the other deposits in Nevada, the Easter Blue was never considered a large producer and changed hands a number of times. It was discovered in 1907 and the first material found was a fine blue color, usually occurring in thin veins, later the mine produced a blue green turquoise with a light to dark brown matrix. A very pretty turquoise when set in silver."

In reality, naming colors is a difficult research task. To elicit your subjets to suggests the Easter Blue name, you have first to be able to present a large mottled spider web with light blue centers in the webbing. …And no, Easter Blue is not in Nathan's on-line color thesaurus. Instead, it suggests you to use Pastel Blue, which is #7FC5EB and not a synonym of Easter Blue. Lots of research still remains to do.

Happy Easter!

Friday, March 21, 2008

More on print services

My post about print services appears to have caused some confusion. While I prefer to get feedback in the form of comments, so others can also comment and a dialogue is established, here are some clarifications — at the risk of making things even muddier.

The first confusion is when the same word is used for something different, a subtle polysemy problem. What we call now the Internet, was called the ARPAnet thirty years ago. At that time Xerox had Ethernet local area networks (LAN) at its sites, and they were interconnected through gateways to create the Xerox Internet. This Internet was a node on the ARPAnet and used the same naming scheme, so it was seamlessly integrated. For example, you could write my email address as or as

PARC was also connected to other networks, like the DecNet, but is was not seamlessly integrated and your email address had to finish in !ucb!parc|beretta to find its way to a gateway from which I could access it.

Thirty years ago was before the general availability of workstations, so the ARPAnet did not have many nodes. However, the Xerox Internet had thousands and workstations. Therefore, the researchers at PARC had to solve all the scalability issues before anybody else was even aware of them.

While the Internet connects logical machines, the World Wide Web hyperlinks documents, using a protocol called HTTP. Initially the Web was mostly text-based, but then its inventor at CERN found out how easy it was to implement a graphical browser on the NeXT system, and the rest is history.

first graphical browser

Next, RPC did not disappear, but it was constantly metamorphing. Here is a diagram of the protocol evolution for services Rob Buckley drew several years ago. It stops at 2000, and now there is a number of web service frameworks, a list of which you can find on the Wikipedia.

protocol evolution for services

A popular way to represent Web service architectures is using the so-called three-tier architecture concepts.

three tier architecture concepts

Two popular models are Microsoft's .net and Sun Microsystem's J2EE.

.net to J2EE model comparison

The jargon on the right hand side can be decoded with this J2 acronym list.

J2 acronyms

Finally, print services are not used just for printing but also for proofing. The latter is somewhat delicate, because the print provider needs to maintain control of the proofing device and the viewing conditions. One approach is to use a remote sensor to assess the ambient conditions and then apply a color appearance model (USP 6,078,732 etc.). Another approach is to use an electronic color proof (ECP) node that mediates the sharing of information about the capabilities of nodal color devices, the interpretation of color image data to the devices, and the control of color reproduction (USP 6,157,735 etc.).

remote printing and proofing

Thursday, March 20, 2008

Blue iris

Iris Blue

A Web color like #333399 is easy to remember. How did I get to it? I went to Pantone's Web page for their color of the year for 2008: Pantone® 18-3943 Blue Iris. There I averaged the pixel colors in the depicted Pantone 18-3943 TCX textile swatch and obtained CIELAB value (23, 27, -53), which in RGB hex coordinates is 333399.

Iris at Gamble Gardens, Palo Alto. (c) Giordano Beretta. All rights reserved.How did Pantone get to this color? On their Web page they explain "From a color forecasting perspective, we have chosen PANTONE 18-3943 Blue Iris as the color of the year, as it best represents color direction in 2008 for fashion, cosmetics and home products," explains Leatrice Eiseman, executive director of the Pantone Color Institute®. "As a reflection of the times, Blue Iris brings together the dependable aspect of blue, underscored by a strong, soul-searching purple cast. Emotionally, it is anchoring and meditative with a touch of magic. Look for it artfully combined with deeper plums, red-browns, yellow-greens, grapes and grays."

That was how they selected it. As for the description of this color, they write "Blue Iris is a beautifully balanced blue-purple. Combining the stable and calming aspects of blue with the mystical and spiritual qualities of purple, Blue Iris satisfies the need for reassurance in a complex world, while adding a hint of mystery and excitement."

Wednesday, March 19, 2008

Print services

Computer science — or informatics, as it is called more appropriately in Europe — has a less linear progress history than other technologies. Indeed, many a breakthrough technology was forgotten only to be reinvented several decades later. I had already posted on concurrent programming (in the comments) and color encoding.

For example, the idea of punching the octal codes of a program on a paper tape instead of toggling it in every time on the console switches was so straightforward it got quickly adopted. But already the idea of using an assembler or compiler to generate the octal codes from a formal language took a bit longer to sink in.

Back in the Sixties and Seventies, when computer users were debating on whether 96 column punch cards were better than 80 column punch cards, computer scientists were busy inventing tools to make their professional life easier by using computer technology. However, the semantic gap from what they were doing to the reality of punch cards was so big, that most of not many of their ideas did not make it into the real world, only to be reinvented thirty years later.

One hot topic at that time was distributed computing. Long before protocols like TCP/IP, HTTP, etc. were invented, things were harder to do and had to happen a step at a time. An example was Grapevine, a multicomputer system on the Xerox research internet. It provided facilities for the delivery of digital messages such as computer mail; for naming people, machines, and services; for authenticating people and machines; and for locating services on the internet. You can read about it in Andrew D. Birrell, Roy Levin, Roger M. Needham, and Michael D. Schroeder, Grapevine: an exercise in distributed computing, Communications of the ACM, Volume 25, Issue 4 (April 1982), Pages: 260-274.

Once we can exchange digital messages and name entities, we can call procedures or invoke methods on a different machine. As we can read in the first paragraph of Andrew D. Birrell and Bruce Jay Nelson, Implementing remote procedure calls, ACM Transactions on Computer Systems, Volume 2, Issue 1 (February 1984), Pages: 39-59,

The idea of remote procedure calls (hereinafter called RPC) is quite simple. It is based on the observation that procedure calls are a well-known and wellunderstood mechanism for transfer of control and data within a program running on a single computer. Therefore, it is proposed that this same mechanism be extended to provide for transfer of control and data across a communication network. When a remote procedure is invoked, the calling environment is suspended, the parameters are passed across the network to the environment where the procedure is to execute (which we will refer to as the callee), and the desired procedure is executed there. When the procedure finishes and produces its results, the results are passed back to the calling environment, where execution resumes as if returning from a simple single-machine call.

The components of the RPC system, and their interactions for a simple call

What was powerful in the Cedar implementation of RPC described in this paper, was that it came with a program called Lupine, which automatically generated the user and server stubs to marshall and unmarshall the procedure parameters into messages. Lupine was so powerful that even a dummy like me could implement a distributed service in an afternoon.

It is not that Xerox did not try to productize this technology. Indeed, it created a product version of RPC called Courier and build a whole network systems architecture on this foundation. As an example, let us look how the first print service product evolved from a research effort.

In the early days of personal computers (PC), printing was very cumbersome. It entailed powering down the PC, carrying the disk to the printer room and inserting it into the PC controlling the printer and booting it up, and finally printing. At the end the printer controller had to be powered down, the disk transferred to the original PC, which could then be booted up again.

In the mid 1970 this lead to the invention of the Ethernet for connecting a PC to a printer's controller and the development protocols to transfer data and control over the Ethernet. The basic concept underlying these protocols was RPC. The main protocol was the PARC Universal Packet (PUP).

In the late 1970s Xerox released a commercial version of this architecture, meeting the most stringent Federal requirements, under the name Xerox Network Systems (XNS). XNS supported a large number of services, among which name, authentication, gateway, time; and filing, mailing, printing, scanning, etc. Like PUP, all XNS protocols were based on RPC, specifically Courier. Later TCP/IP was able to be rapidly developed based on the experience with PUP and XNS.

XNS clients use the Printing Protocol to cause documents to be printed on a Print Service. The Printing Protocol model assumes an abstract printer service which has three distinct processing phases: spooling, formatting, and marking.

A client requests service and, if the Print Service is able to grant the request, the client is given a print request identifier. The Print Service provides status of the job, which the client can request via the identifier, as well as a capabilities ticket (Properties).

The print request consists of a list of links to the documents to be printed, as well as a request ticket (Options). The Printing Protocol includes all security requirements of the Government and a priority. The documents are transferred with the Bulk Data Transfer Protocol. The Authentication Protocol is used for security and the Time Protocol is used to manage time.

In XNS the documents have to be in the Interpress page description language, which can be regarded as a precursor of PDF. An important feature of Interpress is that all pages are independent and can be processed independently in any order, as most suitable for the printer.

XNS Print Service architecture

An important feature of XNS Print Services is to assure that a document printed by different printers will look the same and has the same consistent high quality. To achieve this, the XNS architecture specifies the Print Service Integration Standard (PSIS). The PSIS defines the base case to which all XNS Print Services must adhere to assure compatibility. The principal areas addressed by PSIP are: Interpress level, character encoding, naming syntax, font usage, file usage, minimal service provisions, color encoding, and Printing Protocol usage (exception handling).

Tuesday, March 11, 2008

Roaring silence

As I mention in my green description block on the top of this page, I am relating you a view from my window. From the window of my corner cubicle I see the entire Silicon Valley. A little closer, beyond that empty parking lot that is the constant reminder of better times, I see HP's Corporate Headquarters.

As Nathan wrote in his two previous posts, last Thursday afternoon we had quite a big event there, announcing the new reorganized HP Labs. In addition to the speaches to the press from HP's top brass, there was also an Experience Zone with demonstrations of HP's most advanced research projects.

Interestingly, the morning of the same day down the road in Cupertino, Apple also had a press event for their iPhone SDK. By comparison, when I look through Friday's newspapers, the HP Labs event has been received with a roaring silence. It is not that we did not try. For example, the widely reported idea of shaking the iPhone to delete the pictures is not much cooler than Chandra's blackboard shaking off a heat-generating traditional data center.

If you do not want to click through all the goodies in the HP IdeaLab, you can watch a nine minute summary video on Tom Foremski's IMHO blog post 90 minutes of HP Labs reboot in about 9 minutes…. If you want the full information, including the press kit, you can find it on HP's communication page.

As I am writing this, I am on the phone with Prof. Lucia Ronchi, who told me a related story. Kitty corner of her house in Arcetri, next to the National Institute of Optics founded by Galileo, there is a salumeria (a store selling cold cuts). About 20 years ago, they were selling the salami wrapped in rather old paper, until one day a scientist from the Instutute had a closer look at the paper. He asked the butcher from where he got the paper and was shown a trunk full of papers they had discovered in the basement. The papers were Galileo Galilei's original manuscripts.

Did the journalists just use the HP event to wrap their salami?

Why is this noteworthy? In a place and time when for the past 25 years corporations have butchered their research labs, HP announces that its central research lab will refocus to do more fundamental research. This will lead to new technologies on whose basis new divisions can be built and the comany can be grown faster than the competition.

This is something that goes against the flow here in the USA.

Indeed, Sunday evening I was watching the weekly business report on NHK. They were reporting on the two floods of dollars currently flowing into the Gulf States. The first are the petrodollars from Americans filling their gas guzzlers with gasoline from petrol costing $109 a barrel, the second from us tax payers through companies like KBR, who are assisting our government in the war against terrorism and also buying the services for the Iraq's reconstruction in those countries.

about California

Then a Japanese government representative gave a long explanation in front of a map of America on something about California, because our state was highlighted. Unfortunately he was talking too fast for my rudimentary Japanese for me to make sense of what he was saying.

Then they interviewed some top economists from a Gulf State financial institution. They explained how they were swimming in dollars and how hard it was to make those funds useful to humanity. Their institution had decided to pick countries with a high intellectual potential, i.e., where a lot of highly educated people could put the funds to good use to invent new products and bring wealth to their nation.

currently financed countries

On a map of the world they explained that these countries are of course those in the Middle East, then Egypt, Spain, Austria, Pakistan, and Korea. They explained some of the projects they are financing and stressed how they are geographically allocating their funds.

Then — and this was the reason for this TV program — they explained how also Japan is such a country with a high intellectual potential. As an example, they pointed at the large quantity of research aiming to invent new sustainable energy sources. Consequently, thir investments are now also flowing to Japan. Interestingly, in the above map America , i.e., the dollar countries, is not represented.

new set of countries with investments

In this context, last Thursday's event at HP was very unorthodox to have happened here in the USA. It shows that HP is better aligned with the world than the rest of the big American companies. And we who are doing this high risk work to better humanity are better citizens of the world.

And now feel free to print this page on your HP printer and use it wrap your salami.

Tuesday, March 4, 2008

Encoding color

No matter what color space you are using, how you are compressing an image's spatial content, and in what file format you will encapsulate your image, you have to choose a color encoding standard. In this post I will write about color encoding.

One of the first color encoding standards had been proposed by Xerox in their document XNSS 289005 dated May 1990 and based on their earlier Raster Encoding Standard, which was the basis for Interpress. Color coordinates were normalized to the [0, 1] interval, but not constrained to it, to allow for the correct representation of out-of-gamut colors. For each image and each color channel, offsets and scaling factors where specified to represent the coordinate values with a certain number of bits.

In the Eighties personal computers were slow and had little memory, so efficiency was very important. It turns out that if an image is represented in the CIELAB color space with a realistic gamut, 8 bits are sufficient to store a color coordinate with sufficient precision to avoid artifacts. We then invested a considerable effort in decoding the color coordinates in a the fewest possible number of clock cycles. To implement a color management system you had to be a Cedar wizard. You also had to have a very good understanding of scientific computing, because the Xerox Color Encoding Standard also had the concept of tolerances as integral part of encoded color.

A few years later a much more pragmatic approach was taken. Color had become sufficiently cheap to be used in the office and it was necessary that an ordinary engineer be able to implement a color management system. The thinking was that by then almost all CRT monitors used the ITU-R BT.709-2 primaries, had a D65 white point, gamma 2.2, and achieved a luminance level of 80 cd/m2. With this one could require all input and output devices should be build according to this specification, and then simply normalize the RGB coordinates to [0, 225] and forget about color management systems. For good measure, the gamma non-linearity was thrown in the encoding (before, for efficiency we used only linear color model operators and did the gamma operation in firmware in the display controller).

This sRGB trick worked well for a decade. However, today, after 45 years of R&D, LCD displays have taken over and CRTs have virtually disappeared. LCDs do not have a gamma and do are not limited to the ITU-R BT.709-2 phosphor gamut. For the backlight unit (BLU) typically an active local-area dimming (ALD) direct-array of LEDs is used. These LEDs have as much as 70% external quantum efficiency and use multi-spectrum phosphors to generate a very wide color gamut.

As an aside, today's LCD technology is so fast, that color-field-sequential approaches are again considered, which eliminate the inefficiency of color filters in the panel.

Today's panels have a depth of 12 bits in each channel, a gamut that almost reaches the visual system's gamut, and can blast out 500 cd/m2 or more. True, your visual system is in film mode and you will adapt to the display, but if you just send sRGB coordinates to the display, it will look very ugly. When a modern display is unleashed, color must be managed.

Furthermore, a modern consumer digital camera can capture up to 14 bits per channel. Why do you want to throw them away by encoding your images in sRGB? Keep at least 12!

How then should you encode your color images? Fortunately there is no need to reinvent the wheel. The people in the digital effects business had to deal with these issues many years ago and developed several high dynamic range (HDR) color encoding standards. Most display controllers support at least one of them in hardware, namely Industrial Light and Magic OpenEXR (EXR). Open here refers to the C++ source code published by ILM for reading and writing OpenEXR image format files.

To learn more on this topic, Greg Ward's white paper High Dynamic Range Image Encodings is a good starting point.

Saturday, March 1, 2008

Maya blue paint: an ancient nanostructured material

I must be going through a blue period. After posting on the Blue Hour and just the day before yesterday on International Klein Blue, yesterday's New York Times brings us The Grim Story of Maya Blue by Kenneth Chang (subscription required). Nathan tells me I have to post about it. On the Web, Maya Blue is color #73C2FB.

Maya Blue

Yoko on top of the pyramid, Chichén Itzá in YucatánI will not write about Chaak, the rain god, and of human sacrifice. You already read that in yesterday's newspaper. In fact, we happened to visit Chichén Itzá in Yucatán back in 1994 and nearby we even visited the Cenote of Sacrifice shown below at right. The guide explained us those sacrifices, noting they were only performed as a last resort during draughts.

Until 1993, Maya Blue paint was a mistery, because it survived the harshest conditions in the jungle, and even modern acids, without fading. No need for Ingeborg Tastl's Fading Tool when you use the original Maya Blue pigment!Cenote of Sacrifice

The mistery was solved by Constantino Reyes-Valerio (1922 - 2006), who is also the creator of the Maya Blue Web site. His research revealed that the indigo dye from the leaves of añil was encased in a superlattice of palygorskite, a magnesium aluminium phyllosilicate. He contributed the beautiful image below at left.A warrior with Azul Maya on the background. Constantino Reyes

You can read about the science behind this paint in the Science magazine of 12 July 1996 in the article Maya Blue Paint: An Ancient Nanostructured Material by M. José-Yacamán, Luis Rendón, J. Arenas, and Mari Carmen Serra Puche (subscription required).

They describe that the añil dye was obtained from the sprigs of the xiuquilit (indigophera sp.) plant. However, the superlattice of palygorskyte mixed with indigo molecules does not explain by itself the color tone of Maya blue.

They found that the low concentration impurities of Fe, Mn, and Cr must also be present. Indeed, metallic and oxide particles of nanometer dimensions can strongly influence the optical properties of a material, and small impurity concentrations are sufficient to produce particles.

Science 12 July 1996Nanoparticles can have both linear and nonlinear optical properties. Linear absorbance of small particles can create a resonance feature related to surface-plasmon excitation. The main effect of the particles is classical in nature, although quantum effects are not excluded. Particles much smaller than the wavelength of visible light have an extinction spectrum dominated by the imaginary part of the refractive index. The blue color comes from an absorption curve peaked in the visible part of the spectrum. The oxide metals can account at least in part for the color. In addition, many of the particles are nonspherical, and planar defects may play an important role in the optical properties. The color of Maya blue could be at least partially associated with the presence of nanoparticles.

The authors further report that it is likely that impurities were added to the indigo during the preparation of the añil (heating clay in añil at 100ºC). Oxidation or encapsulation of particles in the substrate explains the acid-resistant character of the paint. The indigo molecules encapsulated in the palygorskite pores probably also contribute to the final color. The combination of an intercalated clay forming a superlattice and the metallic and oxide nanoparticles supported on an amorphus substrate makes the ancient Maya blue look like modern nanostructured materials.

Maya Blue