Tuesday, December 24, 2019

What is the most accurate color wheel?

I received a question the other day. This happens to me all the time. Just a thought here... Maybe I would get fewer questions if I pretended to be ignorant rather than all this pretending to be an expert? I will have to talk with an image consultant about that.

Here is the latest example of things that people want to know.

I have a question for you. I understand that there are different color wheels for different subjects. ... I haven't noticed before...there seems to be two "main" color wheels, but which one is the most accurate?

With the wheels that have 12 colors there seems to be two that come up - one with a red-orange and no magenta, or one with a magenta and no red-orange.

Which one is more accurate? Or are they both accurate but for different reasons?



I have a lot to say on this topic -- enough that I will break it up into two blog posts. In this blog post, I will look at various color wheels, with a eye toward the underlying theory. In the subsequent blog post, I will look at the more general question of the utility of color wheels in general.

Red, blue, and yellow primaries

Here is a color wheel that does not have magenta. This beautiful little color wheel with 72 spokes dates back to a book by Michel Eugene Chevreul in 1839. He was a chemist involved in the dyeing of carpet. His work on color perception came out of trying to understand why dyeing did not always turn out as one expected. This color wheel was his first step in understanding color.

This is kinda pretty, but the left-hand side of this color wheel is a bit dark for my taste. It could be that the colors faded -- after all, this book was made in 1839 afterall. Or it could be that the creation of the color plates suffered from the fact that a good magenta pigment wasn't invented until 1858.

The image below (on the left) is a black and white version of Chevreul's color wheel, with color words for each of the 12 basic colors. Each of these 12 colors are subdivided into 6 steps to make a total of 72 colors in the wheel. At the right, I show my colorized interpretation.

I drew a little triangle inside my rendition to make a point. The colors red, blue, and yellow are all explicitly called out, and are conspicuously 120 degrees apart. The Chevreul color circle is based on the artists' primaries, red, blue, and yellow.

This color wheel satisfies Ashley's first criteria: "one with a red-orange and no magenta". RO is red-orange, and VR (violet-red) appears maybe somewhere around where magenta might be. Perhaps if the color name magenta existed at this time, it may have been incorporated into the color wheel, but I haven't had the opportunity to query M. Chevreul on the topic.

Red, green, blue primaries

My computer monitor doesn't use the artist's primaries. For some silly reason, it uses red, green, and blue. (Note to self: I need to contact those people who design computer monitors and televisions and screens for cell phones and tablets. They need to learn about the artist's primaries, because clearly that would be a much better way for them to encode color.)

I did a little playing in PowerPoint (my graphics design program of choice) and came up with my own  twelve step program... err, twelve step color wheel. I hope that everyone reading this takes a moment to step back and say "ohhhhhhh...." in appreciation of my epic artistic skills.

The Seymourian twelve-step RGB color wheel

For those interested in the details, the red, green, and blue anchor points are (255, 0, 0), (0, 255, 0), and (0, 0, 255). The halfway points between them are yellow (255, 255, 0), cyan (0, 255, 255), and magenta (255, 0, 255). I filled in the points between using HSL coordinates. The hue of HSL goes through steps of 21.3333 from 0 to 235.

This color wheel fits Ashley's second criteria: "one with a magenta and no red-orange". The magenta is at the very bottom, and there is red, and there is orange, but no steps in between.

Cyan, magenta, and yellow primaries

I have a little bonus for those involved in my twelve step program: a color wheel that is specially designed for anyone involved in printing. Here we see that the basic colors are cyan, magenta, and yellow. Please note carefully that the cyan-magenta-yellow color wheel bears no resemblance at all to the red-green-blue color wheel. None whatsoever. Completely different.

The Seymourian twelve-step RGB color wheel

That last line was just a tiny bit of sarcasm. I said that as a way to highlight the fact that these really are the same color wheel. Both are based on RGB color theory, which is a simplification of scientific color theory. This is a fascinating and illuminating topic, and one which is worth a whole blog post to itself.

Oh... I should mention one thing here. Cyan, magenta, and yellow don't do so well at getting all colors. Early printers found it was a good idea to add black. Oh yeah, one more thing... When you print magenta over cyan, you don't really get blue. It's usually more of a purple. And when you print yellow over magenta, it's not a good red. It's a little too orange.

As a result... lately there has been a lot of kerfuffle about expanded gamut printing, where you print with CMYK, but then add in orange, green, and violet inks to extend the range of colors that you can get. Or sometimes you use red instead of orange, or blue instead of violet.

The artists' primaries

Allow me for the moment to revisit the concept of artists' primaries on which the Chevreul color wheel is based. I was taught in kindergarten that:

1) Red, blue, and yellow are the primary colors.
2) You can make all the colors by mixing appropriate amounts of these three primaries.
3) Red plus blue is purple. Red plus yellow is orange. Blue plus yellow is green.

The first is more of a definition than anything that you can test. But the second and third are testable. The second is hard to test, but I tested the third one during lab period in kindergarten. An actual image of the results of my experiments has not survived, but a rough approximation is shown below.

Artists conception of the artists' color wheel

I recall presenting my disappointing results to Mrs. Reidhouse, who was the main lecturer in my kindergarten class. I also vividly recall trying to explain to her that the lack of saturation in the pairwise mixtures was predictable using the Kubelka-Munk equation. But I don't recall her offering a cogent counter argument in support of the artists' primaries theory of color. I do recall being told that it was nap time, though.  

I was trying to articulate to her a basic postulate of paint mixing: Mixing pigments will usually lead to a loss in richness (chroma) of color. In other words, you can't get a rich, vivid green by mixing yellow and blue. You can't get a rich purple by mixing red and blue.

If you find yourself disagreeing with this, then I suggest you visit an art supply store. If Rule 2 were correct, then you would generally see beginner paint sets with five different paints: red, blue, yellow, white, and black paints. Maybe you would see sets with more colors premixed, but if you look at the ingredients, you would only see those five basic pigments. There would be no need for any others.

This set contains 12 of the most popular colors in 2 oz (59 ml) tubes, including Burnt Umber, Burnt Sienna, Raw Sienna, Yellow Oxide, Naphthol Crimson, Cadmium Orange, Phthalo Green, Yellow Medium Azo, Cadmium Red Light, Ultramarine Blue, Titanium White, and Mars Black.

Still not convinced? Then take a trip to the hardware store and ask to see their paint mixing equipment. Count the canisters... do they mix all the colors of paint with five pigments, or are the dispensing devices "Available as either 12, 14, or 16 canister turntables"?

Here's another suggestion for those not yet convinced. I put together a little a do-it-yourself guide to printing with the artists' primaries instead of CMY. Visit my blog post, print out the supplied images, and see what kind of results you would get if HP supplied you with red, blue, and yellow ink cartridges.

In order to get a full range of colors, you need to start with a variety of pure pigments that cover the full range of colors. The theory of the artists' primaries is just plain wrong. 

Red, yellow, green, blue, and purple primaries

Albert Munsell was a smart guy when it came to color. As proof, there was once an upstart wannabe color guru who was so bold as to refer to Munsell as the Father of Color Science. Munsell devised a color wheel that he actually manufactured with paints. (Before I go on, I need to say that his color wheel, was just part of the Munsell color space.)

Munsell started with five primatries. There were an additional five secondaries squished between those five primaries, and each of those ten hues had ten levels in between. Munsell's color wheel thus had a total of 100 different hues.

My rendition of the Munsell color wheel

I want to share a bit about how he created his physical actualization of the color wheel. I share because this is interesting and not well known. Part of this is reverse engineering and presumption on my part. If I have errors in this, I would be happy to recant.

Munsell started with five primaries: red, yellow, green, blue, and purple. With the exception of purple, he had pigments for each of these that he felt truly exemplified the colors. He had to mix two pigments together to get purple, but I mean, how could he avoid purple?

Next he used a creature known as a Maxwell disk to find complements to each of his first five primaries. This spinning disk would have a portion colored with one of his primaries, like red, and another portion colored with a potential shade for the compliment. The complement of red he called "BG" or "peacock blue". He would adjust the pigments mixed for the second pigment until he attained a gray color when the disk was spun.

The ten basic colors in the Munsell color space are listed below. The primaries are in bold type, which coincidentally all have single letter Munsell hue names. Note that Munsell made these with 8 different pigments.

Munsell hue
Color name
Venetian red
Orange cadmium
Raw sienna
Grass green
Emerald green and raw sienna
Emerald green
Peacock blue
Viridian and cobalt
Purple madder and cobalt
Purple madder

(From Albert Munsell, A Color Notation, 1919. Pigments are from paragraph 104, pps. 66 – 67; common color names are from paragraph 58, page 35. I received an email from Robin Myers which recounted the formulations for the ten basic colors that were used in the 1st, 2nd, 4th, 5th, 6th, and 7th editions. The only change over that time was that in the first two editions, 5BG was made with viridian as the only pigment, and later editions mixed this with cobalt. I appreciate having the help of experts like Robin to make sure that my blog posts are precise!)

Red, yellow, green, and blue primaries

A quick review...

The Chevreul color wheel and its derivatives is based on the dubious assumption that red, blue, and yellow paints can be mixed to make all colors. The RGB color wheel is based on the primaries RGB that work well for computer monitors and televisions and cell phones and tablets, and have always worked well in coordinating my underwear. The CMY color wheel is based on the colors of inks that seem to work well, but you almost always want to at least add black. Then you have the color wheel based on Munsell's color space, which in turn was based on a set of paint pigments that Albert Munsell decided upon back in the early 1900's.

These color wheels are all based on the color capabilities of physical stuff. Which is a bit odd, since "color" is largely a function of the spectral response of the cones in the eye, and the brain's processing of the signals from the cone.  It would seem that a color wheel would best be based on what goes on inside the human head, doncha think?

Ewald Hering proposed the idea of color opponents in 1892. His theory was that we sense an object as being reddish or greenish, but never both. There is a continuum of red to green where every color falls. Similarly, there is a continuum from blue to yellow. All color are perceived as somewhere on this continuum. Finally, there is a third such continuum between white and black. This general idea has been borne out with what we have learned about how the cones in the eye and the neurons leading to the brain work together to create color perception.

This idea was incorporated into the color wheel of the Natural Color System (NCS) shown below. This system was developed by Anders Hard and first described in 1966. The rendition below shows 40 steps. The NCS color system is perhaps not as well known as the Munsell color system, but both companies are in existence today, both selling books of colors.

This idea of color opponents (red vs green, blue vs yellow, and white vs black) can also be seen in the design of CIELAB, shown below.

Image from XRite website

I won't say much about CIELAB in this blog post, partly because I am getting tired of typing and suspect that most everyone is getting tired of reading. But, I think I can get away with not talking about the CIELAB color wheel, since I don't recall ever seeing a color wheel that was explicitly built on CIELAB. I say this not to diminish anything about CIELAB.

So, what's the answer?

Which one is more accurate?

The color wheel based on the artists' primaries is not bad, but it is based on a flawed proposition about the primaries.

The RGB color wheel works well for colors on a computer screen. The CMY color wheel works marginally well for printed colors. The two together are compatible, which makes them a very good conceptual model.

The color wheels based on the Munsell and the NCS color systems both have a great deal of research built into them, and accurate physical renditions of each can be purchased. They are both a bit of money, but they exist. And  I would call either of these accurate.

I will leave this discussion for the time being. But beware, I will have more to say..

Tuesday, September 17, 2019

Music soothes the savage Lactobacillus helveticus

I'm sure you saw the news item. The one about how exposing cheese to different types of music during its formative years can give cheese distinctive flavors? It was determined that hip hop music is best, that is, if you like a cheese with a fruity flavor.

It's a compelling thought. On the one hand, it's silly and ridiculous since bacteria don't have ears (like corn does). And even if the bacteria did have ears, does a wheel of cheese have enough sentience to distinguish between The Magic Flute and Stairway to Heaven? I mean, if I have a good hangover going on, I would be hard pressed to tell the difference!

On the other hand, sound is energy. Pick the right range of frequencies, and it can be translated into heat, which (I assume) could change the flavor of the cheese. Sound is also mechanical energy. If you hit the right frequencies, you presumably could set up standing waves that encourage some sort of structure to the cheese. Or maybe there are polymers in cheese that are long enough to have resonant frequencies in the audible range?

I dunno. Maybe cheese is just smarter than we give it credit for. After all, just look at how intelligent Wisconsinites look with cheesehead hats! (Due to the family friendly nature of this blog, I have decided not to include pictures of fans wearing the classy cheesehead bra. Google it if you are interested. It really is a thing.)

The general idea of the experiment

The cheese maker Käsehaus K3 in Burgdorf, Switzerland placed nine wheels of Emmental cheese in nine separate crates for aging. The wheels were exposed to various sounds over the next six and a half months. One wheel got 24/7 of Led Zeppelin. Another got Mozart. Still others got hip-hop, ambient, and techno. Three cheeses had to suffer with a rather constant tone. Finally, one cheese got peace and quiet. This was called the control group.

After six months in these boxes, judges did a random blind assessment of the cheeses to assess whatever it is that official cheese assessors assess. From the images below, it would appear that olfaction is 80% of it. The assessments were repeated, and the results were consistent. Here is a quote from the Reuters article: "Beat Wampfler, the cheesemaker behind the project, said the cheeses were tested twice by the jury and both times the results were more or less the same."

Photos of the judging from the Käsehaus K3 website

What the media has to say

Many news outlets have covered this groundbreaking experiment. Here is a sampling of the reports of the findings.

From NPR: "[The  professional food technologists] concluded the cheese wheels exposed to music had a milder flavor compared with the control cheese. The group also determined the cheese that was played hip-hop had "a discernibly stronger smell and stronger, fruitier taste than the other test samples"

From Smithsonian: "The experts said A Tribe Called Quest’s [hip-hop] cheese was “remarkably fruity, both in smell and taste, and significantly different from the other samples.

The best music to age cheese by

From Reuters: "“The differences were very clear, in term of texture, taste, the appearance, there was really something very different.”"

Well. That certainly sounds conclusive.

Digging a bit deeper

Before I continue, let me say this. I love this work. It's offbeat (no pun intended) and innovative. It opens the way for a better understanding of how things work. It rests in the cracks between science and craft.

On the other hand, I hate to be a spoilsport, but I am skeptical. Hip-hop?!?!?! Really?  I'm not so much a fan of hip-hop, and I like cheese. A good cheese should have the same taste in music as I do. This all creates cognitive dissonance in my little brain.

So, I swam upstream to read a more first-hand-ish version of the results. Here is the original press release, and here is a website version of the experiment.

They did some good things, by which I mean, they used some Science. Here is one thing: "The milk was produced by the same farmer and was processed in the same kettle on the same day of production."

I have already mentioned another thing that they did right. They repeated the assessments and concluded that they were in agreement, that is, the differences weren't just because of the variability in the humans smelling the cheeses. I couldn't find the actual assessment data, but I will assume that they applied the right stats on the assessments to verify that the judges agreed. (That might not be a good assumption, of course. Statistics is a slippery subject.)


All that said, here is a quote from the original press release.

In general, it can be confirmed that the discernible sensory differences detected during the
screening process were minimal. The conclusion that these differences did indeed confirm the
hypothesis, namely that they can clearly be traced back to the influence of music, is conceivable,
but not compelling.

This is common statistics-speak. I will translate for the non-statistician. They started with the hypothesis that music can affect the maturation of cheese and set out to either prove or disprove it.

My professor for Stats 101 +/- 2.7

One possible outcome would be that the judges all said the cheeses smelled and tasted the same. The conclusion would be that, at least for this particular combination of cheese type, music selection, and means for delivering the music, the music has no effect on the cheeses.

Another possible outcome would be that the judges may have agreed that there is a difference between at least some of the cheeses. Upon hearing this, the conclusion from a typical layperson might be "Aha! Music causes cheese to age differently!!" The comments in the articles from NPR, Smithsonian, and Reuters all promote this conclusion. It makes for good headlines.

But a statistician is more careful with the analysis of the results. The faithful statistician is open minded to other possible interpretations of the data. A statistician concludes that the experiment does not disprove the hypothesis that music influences cheese flavor. While English majors abhor this double negative construct, but it is key to critical thinking to see the difference between "does not disprove" and "proves".

The statistician recognizes that "music affects the aging cheese" is one possible explanation for the outcome, but there could be other explanations. Here are some alternate explanations, some more plausible than others.

1) There are several pictures where the wheel of cheese has a placard that identifies the type of music that it listened to. Did the judges see the placard? (This is unlikely. The website says that they followed ISO 13299, which precludes any presentation of the samples that might identify individual cheeses.)

2) I noticed from the pictures that all the judges appear to be together in the same room. Is there a possibility that one judge picked up non-verbal cues from another judge?

3) Quoting from the original press release: "the discernible sensory differences ... were minimal". Hmmm... Maybe the differences were due to subtle differences in the way each cheese was processed? One of the cheeses was probably poured into a mold first, and another was poured last. Some of the cheeses were aged closer to the ceiling, and some closer to the floor -- there is likely a small difference in temperature. Some were closer to the door, which might open the door to more airborne bacteria. Perhaps one cheese received a little more personal attention (and/or bacteria) when workers did their routine inspection?

I don't claim to understand the potential causes of variability in the manufacture of cheese, and I am certainly not casting aspersions on the folks at Käsehaus K3. I just know that there are causes of variability in all manufacturing, however small or large.

4) Were the results analyzed for statistical significance? I say this because people are not good with statistics. Without rigorous statistics, we almost invariably jump to conclusions. Statistics is a tool that forces us to make sure those conclusions are valid. I did not see any detailed description of the statistics that the researchers applied to the assessments, so either the analysis of consensus was minimal or they recognized that the audience would be bored with it, since people are not good with statistics.

5) Were the results analyzed for statistical significance? I say this because the website lists only eight judges. Don't get me wrong. I commend them for putting this level of effort into the experiment. But, consider the fact that a rigorous poll or pharmaceutical test will survey thousands of people in order to provide statistically valid conclusions. But, don't get me wrong. I'm not saying "those darn cheesemakers really should have hired a thousand cheese testers." I am saying that we need to review the data in light of the statistical significance due to the limited number of judges.

6) Were the results analyzed for statistical significance? I say this because they have included a control cheese which didn't listen to any music. If you are testing whether music affects the flavor of cheese, the "obvious" statistical test would be to determine the variation of the eight cheeses that listened to music, and then test for whether the control cheese is within this variation.

Who understands this tripe, anyway!?!?!?

But, quoting from the website: "Thus, the reference sample was comparatively most pronounced in odor, as well as in taste, whereby here also the sample sinus 2 (medium frequency) was perceived as intensively." The control for this experiment was within the natural variation of the rest of the cheeses, so the hypothesis "sound has an effect on cheese" seems to be not supported by this experiment.

My favorite alternate explanation

There is normal variation in all manufacturing processes. The experimenters were careful to make sure that the milk came from the same farm and that the milk was all processed the same way. I am sure that K3 has a standardized practice for making cheese. Good on them. But even in the tightest of manufacturing facilities, there is variation.

That means that some of the cheeses will naturally taste spicier than others, while some will be fruitier -- even if the music was completely feckless. One of the cheeses will be the fruitiest. It could have been the cheese that listened to ambient music, or it could have been the Mozarted cheese. If by random chance the cheese that listened to techno music was the fruitiest, then the articles would all be talking about the effect of techno, rather than the effect of hip-hop.

My favorite alternate explanation is that through normal and random variation, one cheese will be chosen as the fruitiest, regardless of whether there is any effect of music on cheese aging.


Every good research paper ends with a statement like "clearly further research is required to keep the researchers employed". I say that with tongue-in-cheek, but refinement and replication are at the very core of Science.

I was heartened to read this from the original press release: "More extensive testing is required in order to determine whether there is a link between exposing cheese wheels to music as they mature and discernible sensory differences."

The press release goes on to say that tighter controls and more sampling are required. From my previous comments, you could gather that I agree. I would add that rigorous statistics is always a good thing.

I would suggest another experiment: put all the mp3 players on pause, and repeat the 9 cheese experiment. Use this data to better understand the natural process variation.

Tuesday, September 10, 2019

Why are Bermuda onions called "red" onions?

Quora often provides me with suggestions for blog posts. I read a question today that filled me with such indignation that I had to answer it, and had to post this to my blog as well.

Question: Why are 'red onions' called so when they're clearly purple in color?

Bermuda and Spain

Oh! The injustice!! I get angry with misplaced apostrophes, and livid when someone gets all floofy in the spelling of there/their/thay're/thare. But this is more than just word injustice -- this is about color. Anyone who knows me knows that color and beer are the most sacred things in my life.which is as close to being sacred to me as beer is.

But I digress. There is actually a very reasonable answer to this question, and oddly enough, it's one that doesn't require me to call anyone stupid.

In 1969, two linguistic researchers [1] asked a whole lot of people from around the world to name colors in their native language. Altogether, they surveyed a few thousand people, speaking 110 different languages. Based on an analysis of their data, they proposed the theory that languages follow a distinct pattern in the development of color names.

Primitive languages start with analogs of white and black with everything that is a light color being called white (or their word for white), and everything that is a dark color being called their word for black.

Red is the next color that is added, with a single word standing for red, yellow, orange, pink, etc. The next step after red is either to create a new word to separate yellow from red, or to distinguish a collection of greens and blues from white and black.

Ultimately, the language evolves to 11 basic color names: white, black, gray, red, orange, yellow, green, blue, violet/purple, pink, and brown. Some languages (namely Japanese, Russian, and Italian) have further broken the blue category into sky blue and navy blue.

Yes, I understand that my rendition of orange is not so good

Hang on, John. In English, we have sky blue and navy blue. Why aren't these considered basic color names? 

That's a fair question. In English, we distinguish between the two versions of blue by adding the modifiers sky and navy. But, we have a lot of other modifiers that could be applied to blue to arrive at the colors cadet blue, cobalt blue, greenish blue, midnight blue, Pacific blue, pale blue, purplish blue, robin's egg blue, steel blue, and turquoise blue. None of these are basic color names because they are just modifiers of the basic name blue. Chromolinguists also have a requirement that basic color names must also be monolexic, meaning they must be one word.

Getting back to the theory of Berlin and Kay, here is the original sequence, taken from a subsequent paper by one of the same authors [2]:

Original B&K evolutionary sequence of color term development

If this is all true, then it explains the use of red applied to Bermuda onions and also to cabbage which happens to have lots of anthocyanin, both of which are actually purple. At the time when it became necessary to distinguish between Spanish onions and Bermuda onions, the word purple was not commonly used in the language. In the diagram above, the language was in Stage VI. Red was the common term that signified either purple or red, so red was the name given.

The terms red onion and red cabbage stuck, in much the same way as the anachronistic phrases "hit return", "dial your phone number" and "tape a TV show".

Here are some more examples of vestigial chomo-misnomers: What color are your blue jeans?

[1] Berlin, B., Kay, P.: Basic Color Terms: Their Universality and Evolution. University of California Press, Berkeley/Los Angeles (1969)

[2] Kay, Paul, and Richard S. Cook, World Color Survey, Encyclopedia of Color Science and Technology, Springer Science+Business Media New York 2015

Tuesday, August 27, 2019

Where did my indigo (part 2)

I answered a question on Quora recently. What is the true color of indigo? There are many answers to this question. In my last post, I gave one of them: indigo is a dye. This blog post expounds on Isaac Newton's answer.

We all know the seven colors of the rainbow: ROYGBIV. For those who missed that day in kindergarten, this is an acronym for red, orange, yellow, green, blue, indigo, violet.

But, what slice from the rainbow does indigo get? I consulted my high school optics book, Hardy and Perrin. It told me that indigo is the slice from 446 to 464 nm.

Question answered! Indigo is a very specific slice from the rainbow, which has been scienterrifically defined. 👍

But there is more to the story
But, as you might expect from my blog posts, there is more to the story. I didn't mention that this reference book, Hardy and Perrin, was from 1932. I also didn't mention that I had to dig deep to find this definition in any physics textbook. Perhaps I am being just a tiny bit disingenuous by implying that the definition "446 to 464 nm" is today's scientific consensus, when practically every science textbook I could find neglects to define indigo?

I dug my handy monochromator out of the closet and dialed in 455 nm. This is the location smack dab in the middle of the range that Hardy and Perrin gave for indigo, so that should give me the truest indication of what indigo is.

I looked at it and said, "Oh. It's blue." I asked my wife (who claims to be the most color-literate person who I know) what the color was. She said "blue", and then modified it to "cobalt blue", and then pointed at a lovely flower vase of hers. "Did you notice that there aren't any flowers in my cobalt blue vase?" She smiled and batted her eyes. I'm not sure what she meant by that.

I took a picture of the monochromator output with my cellphone camera. There are lots of caveats here, like RGB cameras don't do a good job at measuring color, and computer monitors don't always produce reliable color, but it kinda looks like my camera is identifying 455 nm light as blue.

Hmmmm... Who had the crazy idea of naming that part of the rainbow indigo? Why not just call it blue?

Newton's rainbow
To answer my rhetorical question, Isaac Newton was the person who had the crazy idea of naming part of the rainbow indigo. In 1665, Isaac Newton took leave from his schooling in Cambridge in order to escape the Great Plague. His work over the next two years proved to be one of the most productive in the history of science. Beyond the whole bit about the inverse square law of gravity, and inventing calculus to do that, Newton made some fundamental observations about light during his sojourn.

He passed sunlight through a prism and demonstrated that, among other things,

       white light is comprised of a whole lot of different flavors of light,

        a prism doesn't impart color to the white light that passes through (as was thought at the time), but rather bends light by different amounts depending on the flavor, and

        these individual flavors could be recombined to make white, or to make a host of other colors if some of the flavors are left out.

This remarkable time period is when he labelled the parts of the rainbow, or rather, the parts of a spectrum projectected on a wall through a prism. The results of his experiments were published by the Royal Society in 1672. These results challenged some long-held notions about light and color... but that's a good topic for another blog post.

Blue vs. blue
This may sound like a change of topic, but bear with me here. In English, there are eleven basic color terms (BCT): white, black, gray, red, orange, yellow, green, blue, pink, brown, and purple. I have written about these before when I tried to identify unambiguous color names. These basic color terms have been the subject of much research since the work of Kay and Berlin.

I offer a quote from a brilliant scholar, one who I respect immensely. I just can't say enough about the guy. Here is the quote from the esteemed John Seymour in his blog post How well do we remember color?

"In some languages, such as Russian, Japanese, and Italian, there is a separate word for light blue which stands on its own as a distinct color."

I have another quote, this one from a guy who is actually a real chromolinguist. Again, I respect him immensely. This is from Dimitris Mylonas

"[Two studies]  found that Russian and Greek languages both have 12 BCTs, differentiating ‘light blue’ from ‘dark blue’."

In Russian, we have two monolexic (single word) names for blue: синий and голубой, which mean "blue" and "sky-blue", respectively. In Japanese, the same concepts are in the words kon and mizu.In Italian, there is blu and azzuro. In Greek, kyaneos refers to dark blue, but it could also mean dark green, violet, black or brown. The ancient Greek word for a light blue is glaukos.

Consider the plight of Isaac Newton when he was trying to assign names to the colors of the rainbow. He looked at this wide expanse of colors which slowly pass from violet to green. If he had been conditioned by being a native speaker of Russian, Japanese, Italian, or Greek, then it may have been obvious to him to call the colors violet, dark blue, light blue, green, and so on.

But Newton spoke English. He did not have basic color terms for the two different types of blue. He had three choices.

1. He could use the terms dark blue and light blue. He probably felt this was kinda dorky. Or at least awkward. Or maybe he just wanted all the color names to be monolexic.

2. He could have chosen blue for the dark blue and found another name for light blue. I don't know what color names were in vogue at the time, but today, he might have used: aqua, aquamarine, azure, baby blue, cerulean, cyan, robin's egg blue, sky blue, teal, or turquoise. But these all strike me as being somewhat ambiguous.

3. He could have instead chosen blue for the light blue, and then found another color name for dark blue.

Newton went with option #3, and chose indigo as the name of dark blue. Here is a quote from Newton:

"So there are two sorts of colours: original and simple colours and colours made by compounding these. The original or primary colours are red, yellow, green, blue, and a violet-purple, together with orange, indigo, and an indefinite variety of intermediate shades."

Why did he pick the word indigo? I have a suggestion that I am dyeing to share. If I may be so bold as to quote the blogger who wrote the first post in this series: "Dutch ships carted nearly 170 tons of the [indigo] dye from India to Europe in 1631." Newton did his work with prisms in 1665. Indigo dye was quite popular in Europe at this time. So (my contention) is that the word indigo was at the time associated with a dark blue dye and that it was a common word at the time.

So, indigo is just another name for blue, only bluer than blue can be.

But, why didn't Newton just call them both blue? Why not just six colors for the rainbow? That is the thrilling question I will answer in my next blog post on this subject!

An earlier version of this post omitted green from the list of basic color terms. I apologize to any verdiphiles who were offended. Robin Myers is to be thanked for his ever-vigilant corrections to my blog posts.

Brent Berlin and Paul Kay, Basic Color Terms: Their Universality and Evolution, CSLI Publications, Stanford, California (1999)

Arthur C. Hardy, Arthur C.  and Fred H. Perrin, The Principles of Optics, McGraw-Hill Book Co., Inc., New York. 1932, p. 16

Dimitris Mylonas and Lindsay MacDonald, Augmenting Basic Colour Terms in English, Color Research and Application, Volume 41, Issue 1, February 2016

Isaac Newton, A New Theory of Light and Colours, Transactions of the Royal Society, 1672

John Seymour, How well do we remember color?, John the Math Guy blog, May 30, 2018

Thursday, August 22, 2019

Creating a circle that goes through three points on your lawn

I get some off-the-wall questions once in a while. Today, I got an off-the-porch question and decided the answer might make a good blog post. I'm probably wrong about that, but here goes.

My friend Dark Laser (I have changed his name to protect his identity) is putting a flower garden in his backyard. He wants the edge of the flower bed to be a circular arc that goes through three points . Those three points have been defined by a higher power. Maybe the higher power is his wife, or maybe it's just cuz of where the house is. I dunno. Below is the drawing that he sent me.  I hope you appreciate his obvious artistic skills.

Before he sent the email, Dark did a little googling and YouTubing. He came up with one answer in a YouTube video, which I show below.

I'm not sure how to interpret an email that asks me a question, and also sends me the answer. I'm not sure what he meant by this juxtaposition of Q & A, but due to my insecurity, I took the email as a challenge. "See if you are as smart as this guy, John!!" I am certainly not going to allow any dufus on YouTube to out-answer me on any dumb old math question!

The MathTuber who answered this question used analytical geometry, which lies between geometry (which is all lemmas and compasses) and algebra (which is all factor this polynomial and take the square root of both sides). But mostly the video is algebra.

Here's my opportunity to show off my brilliance. The abracadabra algebra video is all well and good, but it doesn't completely answer the original Dark question. I mean, how does Dark use this equation? Does he need to go out and buy a huge piece of graph paper to lay on his lawn?!?!?

I chose to forego the algebraic approach and go for a solution that is more along the lines of Euclid and his book Elements. A lot of this ancient text has to do with making constructions of various figures with a pencil, a compass, and a straight edge. But I don't think Dark has these tools, especially not in the size required to lay this out on his lawn. So, I improvised with more appropriate tools: rope and stakes.

(While I am at it, let me take a moment for more self-congratulations. Pure mathematicians are perfectly content with theoretical answers. But I am an applied mathematician, which means that my math isn't happy until it answers a real world problem. You can't get any more practical than building an aesthetically pleasing flower bed!)

Step 1

Put stakes at Points 1 and at Point 2. Make two equal lengths of rope, and tie them together at one end. You don't need the ropes to be red and blue, as in my diagram, but it may help.

Tie the other ends of the ropes to the stakes at Point 1 and to Point 2. Grab the ropes where they join and pull them taut. Place a third stake at that point. This third stake is shown as a blue circle in the drawing below.
To avoid any confusion, I use the word stake in a general sense. If any of the stake positions should happen to be on lawn then a tent stake could meet the purpose. If the point is on a wood porch, then a hefty nail or a bolt could work. If the point is on a cement slab of a porch, then maybe a can of spray paint could be used to mark the point. Or a bathroom plunger? 

Step 2

Shorten the two ropes and repeat the process to locate a position for a fourth stake, as shown below as a second blue circle.

Now the aha! part, which I mention in order to create a sense of making progress. All circles which go through both Point 1 and Point 2 will have a center someplace on the blue dotted line! I hope you are as excited as I am.

A practical comment -- If the lengths of the ropes in Steps 1 and 2 are very close to the same, then the two stakes will be pretty darn close together. This is not such a good thing. This will lead to uncertainty in the angle of the blue dotted line, which will lead to inaccuracy in the position of the final circle.

An even more practical comment -- As I wrote that last comment (the so-called  practical comment), it occured to me that in Step 2, you could have kept the rope the same length, and merely pulled it to a position above Points 1 and 2. Too bad you already went through the process of shortening the ropes.  

Step 3

If you want to get technical on me, Step 3, is really two steps. It's a repeat of Steps 1 and Steps 2, only with different points. Repeat Steps 1 and 2 with Points 2 and 3. You probably will need to stretch the ropes out if you already cut them.

The green dotted line in the drawing below is analogous to the blue dotted line. All circles which go through both Point 2 and Point 3 will have a center someplace on the green dotted line! 

I know some of you may have jumped right ahead to the big climax, but I will state it here for anyone who might not have quote caught the significance: All circles which go through Point 1, Point 2 and Point 3 will have a center at the intersection between the blue dotted line and the green dotted line. Assuming the two dotted lines intersect, and assuming the two dotted lines are not along the same line, we have uniquely defined the center of the circle.

Step 4

A pure mathematician would stop at Step 3, since the point has been theoretically defined. But an applied mathematician, being of a superior breed, would realize that we still need a way to mark that physical intersection point on the porch.

Here is my suggestion. Place a skinny pole at a possible location for the circle center. Move the skinny pole around until it lines up with both of the blue stakes. Then turn your head and line the skinny pole up with the two green stakes. Then go back to the blue stakes to make sure they still line up. This may take several iterations. (My own experience suggests that copious quantities of beer can reduce the number of iterations necessary, not because beer increases your skill level, but because it gives you a more realistic view of just how important the position of the center of the circle is in the grand scheme of things.) Put a nail or a stake or a plunger at the point of intersection. 

If neither nail nor stake nor plunger will work on the porch, then buy another 12 pack and set it next to the intersection point. When a neighbor stops by to see what you're doing, hand him a beer and ask him to sit at the intersection point. The extra beers will keep him from moving.

A comment for those who remembered taking geometry... The task of finding the intersection would have been done with a straight edge. If Dark happens to have a 2 X 4 that is long enough, he could certainly use that to mark the dotted lines. A can of spray paint could serve to make that line indelibly, so the next owners of the house can appreciate the mathematics that went into constructing the flower bed. I haven't looked in Dark's garage lately, but I am guessing that finding a 2 X 4 that is long enough is a tall order. Or a long order. So, we must resort to an iterative procedure which would have been scorned by Euclid. But being scorned by Euclid is not a big deal. We are using non-Euclidean geometry.

Step 5

We're now ready to finish the project. Attach a rope to the nail/stake/plunger/neighbor at the center, and stretch the rope out until it reaches Point 1, Point 2, or Point 3.

Tie a spike to the  rope at that point. Holding the rope taut, move the spike from Point 1 to Point 2 and then on to Point 3, scratching the lawn to indicate the edge of the circle. If you are not skilled in the art of lawn scratching, feel free to tie a can of spray paint to the rope. I suggest a color of paint which is different from that of the grass. Although I show purple in the drawing below, green paint would provide a real good contrast to the color of my lawn.

Step 6

Pull up a lawn chair and finish the beer, content in having accomplished a good day's work.

Sunday, August 18, 2019

The allure of tweeny colors

I recently saw an interesting question on Quora about colors that are positioned between the basic colors. Here is the question, and the answer I gave.

Question: “Why are those color hues so intriguing that linger right between two known colors: between blue and gray, between pink and purple, etc.? They keep me captivated with the visual ‘tease’.

Interesting question! I have seen this before, and my own observations are that these tweeny colors are interesting and either beautiful or ugly because of this. I don’t know if I have the answer to why, but I have one plausible explanation.

Basic fact #1: There is much information compression and loss of information as an image makes its way from the retina to the upper parts of the brain. If I look out on the room before me, and then close my eyes to attempt to remember what is there, I come up sadly short. I won’t remember anywhere near all the objects, or remember much in the way of details about them. I certainly wouldn’t be able to paint a picture from memory (even if I could paint).

Basic fact #2: There is evidence that colors work the same way. When the lower brain tells the upper brain that a car is red, it doesn’t report the exact color coordinates of the color either an an RGB value or a number from a color matching book. According to the theory, it will generally put the color of the car into one of a small number of buckets. There might be eleven buckets, or maybe there are just a few more.

I suspect you may be inclined to disagree with such a small number. Surely there are hundreds or maybe thousands of nameable colors? The small number in the last paragraph comes from an experiment where people were shown a color and moments later asked to pick that color out of a lineup. This experiment showed that our remembrance of a color skews toward a quintessential version of that color family, and there are not hundreds or thousands of color families. A somewhat desaturated blue is remembered as blue. A slightly orange version of yellow is remembered as yellow.

Here is my blog post on the experiment: How well do we remember color?

This explanation is consistent with the way we perceive the world. I look at a car and say that it is red, completely ignoring the fact that one part of the hood is lighter because of the position of the Sun, and the lower door panel is darker because it is partially shaded. In some areas of the car, there is a strong delineation in color, and I can easily choose to be conscious of that. In other places, the change in shade is gradual enough that it is difficult to be consciously aware of it.

Let’s apply this knowledge to your question. Consider looking at a car that is somewhere between blue and gray. I may glance at it once, and my lower brain will decide that the color is in the gray family. I look again, and my lower brain may change its mind and put the color in the blue family when it reports to the higher brain.

If this happens, we have a cognitive dissonance - the upper brain has to deal with two conflicting thoughts: “the car was gray” and “the car is now blue”. This conflict draws our attention to the color, hence it is interesting.

Monday, August 5, 2019

Where did my indigo? (part 1)

I answered a question on Quora recently. I am so proud of my astute answer that I decided to expound on it to make it into a blog post.

The question: What is the true color of indigo?

In today's blog post, I provide the first answer to that question.

Dyeing is a pigment of my imagination

The words dye and pigment are often used interchangeably. Just don't try that in the presence of any colorist. At best, they will roll their eyes and/or laugh at you.

Cool pic of dyes from Alliance Industries

The general term is colorants, something that is used to impart color. Dyes and pigments are two types of colorants.

Dyes are molecules (often organic) that are incorporated into fibers. As a rule of thumb, they are soluble, and we work with them typically in solution, so they are individual molecules. Also generally they require a binder molecule to attach them to whatever we are dyeing. Dyes are most commonly used for dyeing fabric. Dyes need to penetrate into the substrate (e.g. the cloth fibers) in order to become permanent.

Pigments are made from grinding stuff up -- usually non-organic compounds. Since they are ground up, they come in the form of solid particles with lots of molecules clumped together. when used, they are generally suspended in a vehicle that is evaporated when the paint or ink dries. The vehicle might be water (as in latex paints and inkjet inks) or oil (oil-based paints and lithographic ink) or a solvent such as alcohol or toluene (sometimes used in gravure printing ink). Pigments generally coat the substrate rather than becoming incorporated into the substrate.

I expect everyone to use these terms correctly from now on. This will be on the final exam.

Mordant or less?

When I was young, I remember my sister showing me a neat trick. She showed me how to crush the flower buds of a certain flower between my fingers. The flower excreted a gorgeous rich blue fluid. My sister told me that this was a dye used by Native Americans.

Naturally, I was scolded. Maybe my mother was angry because the fluid stained my hands. More likely, she was angry that I stained my clothes. Then again, maybe she scolded me because I was destroying her irises. But, my memory is hazy. Maybe it was a wildflower. And maybe the Native American dye that my sister told me about was beets. I dunno which version is true, but one fact is perfectly clear. It was Nancy's fault. She forced me to get into trouble. This last part will be on the final exam.

This all left me with the impression that dyeing was pretty easy. You find some natural color in the woods or in a field. You crush the plant, dissolve it in water, and then soak your cloth in it.

Indigo dye is almost that easy to use. You just soak the cloth in a solution of the dye, rinse it, and then dry the fabric. Well, maybe that's a simplification, but I think I have the basics of it.

But making the dye is a bit more involved. The indigo plant has pretty pink flowers, but that's not where the dye comes from. Oddly enough, the dye is made from the leaves. These leaves are mashed and then fermented. The gunk left over is then dried and beaten to aerate it, since the process needs oxygen. Then it is left to dry into cakes.

When I first heard this, I was surprised. Who'da ever thunk to ferment leaves? Who'da ever thunk to ferment something and then not drink it? That part boggled my mind. (I'll get back to that in just a bit.)

Getting back to the dye, indigo is odd in the world of dyes. Indigo is called a non-mordant dye, because it does not require a mordant.

Ok, so what's a mordant?

Most dyes do not have a natural affinity for cloth. That is, they don't stick. Cloth is treated with mordants (like alum or tannic acid) so that the dye molecules will stick. The mordant molecules have an affinity for both the cloth and the dye, so they bind dye molecule to cloth by linking the left arm to one and the right arm to the other.

Here is the lesson that will appear on the final exam: Indigo was one of the earliest dyes because of two properties. First, the dye is created naturally in a way that humans could readily see and imitate. Second, the dye did not require pretreatment of the cloth to fix the dye.

Who invented indigo?

Indigo comes from the the indigo plant, specifically from the species of the indigo plants named indigofera tinctoria and indigofera suffruticosa. I called up the ancient Roman historian, Vitruvius, to help answer the question of who invented indigo dye. He told me that "indigo comes from India... where it attaches itself as mud to the foam of the reeds." Hence the name, indigo, which is derived from the Latin word indicum, meaning substance from India.

Now I can understand how someone would have come up with the idea of fermenting indigo leaves. I surmise that someone noticed that the muddy foam on the indigo plant stained fingers and cloth. They then sought to duplicate the natural process, and likely found that they needed a bit of this sticky foam as a starter. Whatever animicula was in the foam -- maybe it was yeast? -- would greedily ingest something in the leaves and go through some sort of chemical reaction that liberates the indigo dye molecules.

A bit of historical pedanticness -- just which Roman historian I spoke with is a matter of disagreement among historians. The quote above is from Ball, p. 201. Another account (Phipps) refers to Pliny, without a fancy quote. Another author, DeBonnet, attributes a similar quote to Dioscorides in 23 BC. I am not really sure who I talked to on the phone. I had spent the whole night sampling my fermented indigo, and ... well...

Marco Polo brought this dye to Europe from his travels in India. Indigo dye became a much desired item for import from India to Europe, first along the Great Silk Road, and then around the Cape of Good Hope. For example, Dutch ships carted nearly 170 tons of the dye from India to Europe in 1631. This factoid will not appear on the final exam.

Cool picture of the indigofera plant, from Phipps, 1832

I pause here to admit to a gap in my personal recollection of world history. I'm a bit surprised that the ancient Greeks had trade routes going with India. Here I thought Marco Polo was the guy who first connected European commerce with Indian commerce. Did I sleep through that day in history class?

So far, the story goes like this: The recipe for making indigo dye from the indigofera plant was devised in India, which became the source of indigo dye in Europe. There are reports of indigo dye in Harappan Civilization in the Indus valley somewhere around the time 2,000 BCE, so this all makes sense.

But that's only part of the story. A clay cuneiform tablet, dating back to 600 or 500 BCE, was found in southern Iraq with the recipe for creating indigo dye.

This is a bit of a conundrum having to do with the history of indigo. Suppose you were transporting indigo from India to Babylonia. Would you load your camels or rafts or what-have-you with bundles of leaves, or would you load up with cakes of the processed dye? I'm thinking I would go with the more compressed form. Keep up with me now... so if we have an ancient Babylonian tablet, written in ancient Babylonian cuneiform, that was found in the area that was ancient Babylon... and that tablet gives a recipe for turning indigo leaves into indigo dye...

Do you see where I'm going here? Why would a Babylonian go to the trouble of describing he process to manufacture indigo dye to a Babylonian when Babylonians are only receiving shipments of the processed dye???!?

I think that the indigo plant may have been cultivated in ancient Babylon. I think that indigo seeds were transported from India to Mesopotamia at some point before 500 BCE. Then again, maybe the seeds went the other direction at some time before 2,000 BCE?

Here's another indigo sighting from about that same time period. Herodotus (a Greek historian from about 450 BCE) wrote that in Caucasus "They have trees whose leaves possess a most singular property: they beat them to a powder, and then steep them in water; this forms a dye which they paint figures of animals on their garments." Herodotus doesn't actually use the word indigo, but it sure sounds like he was talking about how to make indigo dye. He also doesn't mention India. Strange.

So, now I'm confused about whether the process to manufacture indigo dye actually came from India.

Let's muddy the waters a bit more. In ancient Egypt, mummies were wrapped in linen. The strips of linen were dyed with indigo. This puts the invention of indigo back to around 2,400 BCE, and perhaps earlier. Did the very ancient Egyptians get their indigo from India? Or did the Indians get their indigo from Egypt? Were there even trade routes between these civilizations at that time? Tell me, just where did the indigo?!!??

There are also early reports of indigo dyes being used in the Xinjiang province of China around 1,000 BCE. Were there trade routes between China and India? Here my meager world history completely falls on its face. I done got edicated in 'murica. We don't need no stinking urapean history there.

Earliest occurrences of indigo dye in various regions of the Old World

I look at the map above, and it seems likely to me that indigo dye was developed independently in Egypt and India, and possibly also in China.

But I omitted one last piece of the puzzle. Indigo dyed fabric was found in scraps of cloth in Huaca Prieta, Peru that date back as far as 5800 BCE! I hope you're as excited about that as I am.

My conclusion: a process to extract indigo dye from the indigofera plant was developed independently in multiple places around the globe. That will be on the final exam.

Stay tuned for part 2 of this series of blog posts, where I investigate Isaac Newton and the indigo that he put in our rainbow!

Want to know more about pigments and dyes?
Have a look at a blog post about mauve, Tyrian purple, and magenta.
Or, check out the blog post about the invention of Klein blue.
Or better yet, have a quick read about vermilion and cinnabar.


Ball, Philip, The Bright Earth, Art and the Invention of Color, University of Chicago Press, 2001

Beloe, William, Herodotus, Translated from the Greek, 1814, p. 254

DeBonnet, Maurice, Origin of Paint Pigments, Varnishes, Vehicles, National Painters Magazine, Vol 48, Jan. 1921, page 26.

Finlay, Victoria, The Brilliant History of Color in Art, Getty Publications, 2014

Mattson, Anne, History of Indigo in the Early Modern World,

Nassau, Kurt, The Physics and Chemistry of Color, The Fifteen Causes of Color, John Wiley and Sons, 1983, p. 285

Phipps, John, A series of treatises on the principal products of Bengal, 1832

Splitstoser, Jeffery C., Tom D. Dillehay, Jan Wouters, and Ana Claro, Early pre-Hispanic use of indigo blue in Peru, Science Advances  14 Sep 2016: Vol. 2, no. 9,

St Clair, Kassia, The Secret Lives of Colour, pps. 189 - 192

Wikipedia, Indigohttps://en.wikipedia.org/wiki/Indigo

Wild Color, History of Indigo & Indigo Dyeing,