“How can you be in two places at once, when you’re not anywhere at all.” I encountered this phrase in high school when my classmates introduced me to the Firesign Theatre comedy recordings. I believe it is an appropriate thought to have when trying to map and understand the organization of pigments by color index number that belongs to the domain of the Society of Dyers and Colourists.
While some hues we see match the color index number across whatever brand of paint you might select, some colors defy this method of organization. I doubt you will not find a brand of oil paint called Ultramarine or French Ultramarine Blue that is not PB 29.
For the uninitiated, pigment manufacturers abide by chemical composition and use cases when registering pigments with the Society of Dyers and Colourists (SDC). This provides a standardization so that end product makers can be assured of some semblance of order in what would be a chaotic, self-determined method of naming pigment hues. The SDC has a “shorthand” method of expressing what pigment belongs in which hue category along with a rough idea of when the pigment was catalogued.
PY = Yellow, PO = Orange, PR = Red, PV = Violet, PB = Blue, PG = Green, PBr = Brown, PBk= Black, PW = White. As you can see Blue “won” the right to use the letter “B” since Brown and Black would also have required the same letter. The numbers next to the color hue record when the pigment was entered into the SDC catalog. When first organized, the ancient pigments received the lower numbers, followed by newer pigments as they appeared over time.
A major part of the SDC cataloging process is to place pigments into the hue group that share the same chemistry. The only problem is that the same chemicals, manipulated in different ways (basically a different “recipe” using the same ingredients) can make a pigment using the same color index number be in two different hue categories. So, using the color index number as the sole determining factor for organizing color groups will not work.
For this essay, I will only illustrate the color index confusion surrounding PB 28 – Oxides of Cobalt and Aluminum. Several paint makers have this color in their oil paint line appropriately called “Cobalt Teal” or “Teal Green.”
However, for those familiar with color index numbers, you are saying, Wait a minute. You are mistaken. PB 28 is our old and reliable Cobalt Blue and you would be absolutely correct. Paint makers are correct in labeling both Cobalt Teal and Cobalt Blue using the same color index number.
What makes matters a bit more confusing is that PG 50 also has a similar hue appearance to Teal Green but it is made with Oxides of Nickel, Cobalt and Titanium, a different chemistry that yield a hue that looks much like Cobalt Teal or Teal Green.
For those interested in the chemical process, high heat is the energy used to combine the elements into a substance that once cooled can be ground into pigment. Cobalt Blue has a chemical formula: CoAl2O4. Adjust the ratio of cobalt and aluminum to some degree and the pigment color resembles a blue-green hue.
Inorganic pigments, like cobalt, have a fascinating history that we will explore sometime in the future. Perhaps the facts and fantasy surrounding kobold ore, German for “goblin ore,” with a focus on the creatures that inhabited the mines will make for a good Halloween time period essay. As always, the “devil” is in the details.
Syntax of Color
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