• Michael Skalka

Cadmium Yellow Deep: A Misnamed Pigment? Part 1

Summary: Pigments with the same Color Index name but appearing to be a different hue is confusing for the consumer. Abiding by the Color Index name seems to triumph over the simple visual evaluation of identifying a hue. Colors cannot be selected by their Color Index name alone. The history of the discovery of cadmium, its properties, and how yellow behaves as an outlier is the subject of this essay.


While it may seem I am picking a fight about the color Cadmium Yellow Deep, read on to learn the whole story. This is the tale of 7740-43-9. When this pigment is reduced to its chemical services registry number, the element named cadmium loses all its charm. Before processing, cadmium appears as “soft blue-white lustrous metal or a grayish-white powder.” (U.S. Dept. of Labor, Chemical Identification, Production and Use.) This description is a far cry from the fiery, red, orange, or yellow pigment that is so integral to many artists’ palettes.


My argument is with the color name cadmium yellow deep and its physical appearance. Nearly every tube of cadmium yellow deep I have come across is a far cry from anything that comes close to being a yellow hue. Honestly, to me, Cadmium Yellow Deep paints appear to be orange in hue. Call it cadmium light orange if you wish, but no matter what, it looks orange. So why do materials manufacturers continue to call it Cadmium Yellow Deep?


I realize that light, medium, and dark (deep) forms of a hue can be subject to objective analysis and discussion about a color’s mass tone, tint, and color bias. Yellow hues have some unique characteristics that bear further examination. It is easy to understand the concept of light and medium yellow, especially when compared to each other. However, what hue is dark yellow? Think about the uniqueness of values related to yellow hues.


Many pigments are low in value by their nature. Yellow, assuming we are visualizing the hue Cadmium Yellow Light, is not one of them. Making nearly any color darker by adding black functions in a predictable way. But as practicing artists, most of you realize that adding black to yellow yields a green hue, not a darker form of yellow. All of the other primary and secondary colors get darker and suffer a loss of chroma with the addition of black. They do not shift to another hue.


I have read some carefully thought-out arguments by artists who state that dark yellow is brown. But, observing many paintings where yellow is depicted in shadow, brown is not the color applied to a painting. So, for now, the mystery of what makes the addition of black to yellow unique in tone and chroma will remain an unanswered question. (Editor’s note: I posed the question of adding black to yellow to obtain a dull green to a world-renowned imaging scientist and a suitable answer was not obtained. More study will ensue.)


While searching for the chemical index name, PY37, that defines the code paint manufacturers use for cadmium yellow deep, I found one humorous result. PY37, in one instance, provides information on a “Chicken and Brown Rice” dog food. Before you get alarmed and contact the Consumer Product Safety Commission, the use of PY37 denotes a stock number for the dog food, not an instance of pet food contaminated with cadmium.


Most references to PY37 focus on the art materials arena. Interestingly, no single pigment solidly defines the color called Cadmium Yellow Deep. Some manufacturers use PY37, others use PY35, which is more typically found as Cadmium Yellow Medium and one manufacturer blends PY35 and PO20 which is Cadmium Orange. That indisputably points to Cadmium Yellow Deep as leaning heavily toward an orange hue.


It appears that cadmium pigments in general, have hue quality control issues. While reading tube labels, (an occupational habit of mine,) I notice that many cadmium colors are blends of two cadmium pigments. I speculate that manufacturers need to do this to establish hue consistency from batch to batch since the colorant as it comes from the manufacturer varies a bit and requires some adjustment to match previous pigment orders.


Cadmium pigments are a microcosm of intrigue and mystery, as are many other pigments. Controversy erupted the moment they were discovered. Like many of the elements found on earth, isolating cadmium came about as a byproduct of another research effort. I suppose it is hard to go into a scientific laboratory and decide that this month’s goal is to discover a new element! These things tend to fall into the category of being at the right place at the right time. Such was the circumstance for the discoverer of cadmium.


Friedrich Stromeyer (1776-1835) was provided with a sample of zinc oxide that was marketed as a pharmaceutical product to the public. Suspecting that it contained a contaminant, Stromeyer analyzed it. At the same time, two medical product inspectors had similar thoughts that the zinc oxide was adulterated and had the material examined. At first, thinking the foreign matter was arsenic, the product inspectors finally concluded that it contained a new unknown metal.


In their official report, the inspectors suggested that the new metal be called Klaprothium after the recently deceased scientist Martin Klaproth. Dedicated readers of The Syntax of Color will instantly recognize that Klaproth was the discoverer of the element uranium in 1789. https://www.syntaxofcolor.com/post/uranium-and-copper-oxide-pigment (SOC published, February 2020.) Klaproth independently verified the existence of titanium in 1792, but William Gregor (an ordained minister in the Church of England and an amateur scientist) who found it first in 1791, easily disputed Klaproth’s claim. Klaproth provided the name “titanium” for this element, but despite Gregor being the discoverer, Klaproth’s titanium was permanently adopted. Had Gregor won the naming battle, we all might be referring to the yellow pigment as Manaccanite Yellow.


Stromeyer became embroiled in a similar controversy with the two medical inspectors, but since he published his discovery late in 1817, he beat the medical inspection team by several months in announcing his find. By “late” discovery, I mean Stromeyer was 26 years late. He probably did not keep up with journal reading.


I cannot pass up the opportunity to tell you that Stromeyer was a student of the esteemed scientist, Louis Nicolas Vauquelin who discovered chromium in 1797. This creates an interesting connection between people and discoveries since chromium-based yellows and reds are the precursors to cadmium pigments. The scientists involved in the discovery of both elements and pigments were part of a very small community.


As stated before, the drive to discover new elements and the means to accomplish those tasks by the methodologies employed was shared by a small circle of brilliant minds thinking about similar issues, in this case, analyzing materials to separate their components and as a byproduct, they discovered new elements, and in turn, others applied their knowledge of chemistry to derive new pigments. I believe that the next concentration of brilliant talent to focus on complex issues did not occur until the middle of the 20th century when scientists gathered to focus on the Manhattan Project which produced the first nuclear fission weapons.


Regarding future leaps of scientific knowledge, I believe the 21st century will usher advancements in the practice of medicine by unraveling the entire genetic code of human beings to develop therapies for diseases or they will create great strides in artificial intelligence machines, and we will end up living the fate that befell the planet in the HBO series Westworld.


Stromeyer named his late discovery of cadmium after the Greek word, kadmeia or cadmia, a term used for zinc carbonate. As the name implies, it has a very close association with zinc. Cadmium production is the result of isolating the element during the refining of zinc, and lead ore copper. So if you encounter an internet scam that offers a great reward from buying shares in a cadmium mine, turn it down without hesitation. Cadmium is only found in nature in greenockite, a cadmium sulfide mineral, but without the quantity sufficient to mine it commercially.


Syntax of Color

(End of Part 1)


Previously Published in the Grammar of Color, Volume 4, No. 1


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