Scientific Color

We can babble philosophically about whether or not what we call "red" looks the same from another person's eyes, we can compare the adjectives we use to specify colors--is it maraschino red or cayenne?--but when we're talking to our computers, categorizing flowers, designing objects for mass production, branding a company, or establishing a flag's official colors we have to be able to be specific about which exact shade of red we want.

i-079de25dd3108289139b5b193b931a15-colorstandards.jpgThese days we have standard color systems that define colors as specified mixes of red, green, and blue pixels on screen, specific mixtures of pigments in paint, or different levels of cyan, magenta, yellow, and black in print but before we could refer to these numerical standards there had to be a central repository that held the definitions of every color and distributed them as reference color dictionaries.

i-62610692d1f9cf448ae5f3651d5cd1b7-horticultural colourchart.jpgThis Horticultural Colour Chart was just such a color dictionary, prepared by the Royal Horticultural Society in 1938 for use in identifying and matching flower colors. This standard was used for decades in horticulture and in other scientific disciplines that needed to be precise about color, in particular analytical chemistry, where identifying chemicals based on how their colors changed in response to different processes was a common technique. How did this old timey chart find its way into my lab, more than 70 years later?

i-2f26294653ac84b044f89c72aa8a6427-pinks.JPGFor that we have to thank my labmate Jake, whose passion for all the old-timey things in life has extended out to the experimental techniques he chooses. Jake is using synthetic biology to make different chemicals in yeast and needs to be able to identify which compound his yeasts are making when different metabolic enzymes are added or taken away. For this there are a lot of methods that can separate chemical compounds and identify them, most based on the principle of chromatography.

i-7d8a33fd9dd1ee85145f29673c6d7689-TLC_black_ink-thumb-300x225-57154.jpgIf you draw a dot in black ink near the bottom of a piece of paper and place the bottom of the paper into water just below where the dot is, the water will slowly creep up the paper pulling pieces of the ink up with it (try this at home!). Black ink is made up of many different colors mixed together, and each of the colored pigments will travel a different amount up the paper, separating the mixture into its individual colors--hence chromato- meaning color and -graphy meaning writing in Greek. Chromatography can be done even on uncolored compounds, but there has to be some way to visualize how far up the paper (or more often some kind of silica gel) they have travelled, which can be done by shining UV light (think CSI) or by adding reagents that cause a visible color change. Nowadays, chromatography is often done by machines filled with tiny capillary tubes instead of on paper, separating out mixtures based on many different properties, then sending them off to many other sophisticated machines that can determine the identity of the individual components.

Jake, of course, would never want to use such fancy modern equipment when there is an antique option available. Instead he's using the thin-layer chromatography technique where the compound is spotted on the bottom of a layer of silica gel which is then dipped in a solvent, allowing the spot to to travel up the length of the plate and separate out. To visualize the constituents of his chemical mixtures he's using the van urk-Salkowski reagent (PDF) which reacts with many of the compounds he's interested in and turns bright colors depending on what chemical is present. Each of the colors is matched against the official Horticultural Colour Chart, listed in the original paper with the exact page number where it the color can be found.

i-aa0a8a2c3800cd768aa0243fecc1ea14-colormatchtable-thumb-510x189-57158.pngThere are dozens of compounds, each with a very descriptive color matched to it, allowing you to relatively quickly (but not too quickly) identify what is present in your mixture.

i-de9cf8bd8b39fa924495bc195b0995f0-rainbow.jpgI may joke around about Jake's old-timeyness but there is something valuable in being able to do these kinds of procedures with tools that don't cost half a million dollars, something really beautiful about Jake's color chart, and something so fun about thinking about old standards and how new tools can often necessitate new standards to go along with them.

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Blueness doth express trueness. -Ben Jonson

By Peter Gold (not verified) on 20 Oct 2010 #permalink

I used thin layer chromatography in a CSI type lab class I taught to match the color of pens used in a "crime" It was fun!

Great blog post! Although I do like big and fast machines, I have an appreciation for more "hands-on" stuff. It tends to be elegant, clever, and aesthetically appealing.

There are international standards for just about everything, but not, to my knowledge, color. I would think that primary colors could be defined by their wavelength, so when a red, for example, was specified, everyone of interest would be able to repeat it.

By Brett Fox (not verified) on 22 Oct 2010 #permalink

Brett (comment #4) - that's what the CIE was established for. In the 1930's of course, they were more worried about the new fangled technologies of colour photography and printing, but it's the same CIE who's standard "primaries" are used to describe the behaviour of your monitor to your computer via a colour profile.

As for a database of names to spectra (which I assume is what you really mean by "wavelength") that simply wouldn't work for cultural reasons: where we see one colour ("blue") other cultures may see two (Russians see "seeniy" and "golubiy").

By Ian Kemmish (not verified) on 25 Oct 2010 #permalink