Winter is slowly slipping out of our grasp, the new realities of 2018 are finally settling into place, March is already upon us, and oh my goodness I need a second to catch up. A moment of reprieve, a source of grounding, and yeah, probably a double whiskey neat. The earth itself, what with gravity and all, is the most grounding thing I know. With Capricorn season far behind and Taurus a month away yet, I’m feeling the need to refocus and establish this grounding for myself. How, you ask? Earth pigments, of course. Let’s talk about them.
A "flight" of ochres ranging from light yellow to purple from StudioLab's Material Archive
1: Yellow Ochre Light | 2: French Yellow Ochre (besides "France," source unknown) | 3: Transparent Gold Ochre (source unknown) | 4: Luberon Red Ochre | 5: Armenian Crimson Ochre | 6: Armenian Purple Ochre
To introduce our band of players, we’re talking about iron oxide, red earth, yellow earth, ochre, umber and sienna, that can range from light yellow all the way through rich oranges, reds and browns (oh my), and even blue, violet or black. Earth pigments are crude ores colored mainly by iron, but also by other metals, which are mined, washed, pulverized, and sometimes heated to produce different hues (Gottsegen 136). We'll talk about processing stuff later. There is a common misconception that earth pigments are organic, which, although false, is a valid progression of thought. Earth, natural, organic– these terms all fit into a similar category in our minds. However, organic refers to the chemical class pertaining to or deriving from living matter, plants and animals, and extends to all carbon-based compounds. On the other hand, inorganic refers to the stuff that’s not derived from living matter, and isn’t based on carbon. Dead stuff that was never alive to begin with. Minerals, metals, salt complexes. Earth. Hematite is the most commonly identified iron oxide in red earth pigments, and the iron oxide hydroxide goethite is the most frequently found iron compound in yellow earth pigments (Berrie 39).
Gorgeous hematite specimen that lives in StudioLab's Material Archive. Sourced from Kremer Pigments.
Along with the major categorical divide of organic and inorganic, pigments in both classes can also be described as either natural, synthetic, or somewhere in between. As with most pigments, the nomenclature for iron oxides has been erratic and inconsistent over the years. Iron oxide is the broadest descriptor, referring to all natural and synthetic pigments that contain mixtures of iron oxides and oxide hydroxides. Earth describes iron oxides pigments that are sourced naturally, a subcategory of which is ochre, which comes from specific quarries also containing kaolinite (china clay) and quartz. Umber is the name for a slightly different chemical class that contains manganese in addition to iron. Heavy metal. Sienna falls somewhere in between ochre and umber, and has the well known Tuscan city to thank for its namesake (Berrie 40).
Time for a little game. Visualize yellow ochre on your palette, alongside raw sienna– I’m seeing it now. What differences do you notice in the hues? The temperature? The tinting strength, perhaps? The luminosity? Do you have a clear picture of how each pigment behaves?
Aqueous pigment dispersions in Acrylic 50H Binder, all products from Guerra Paint & Pigment Corp.
Alright, I'm not going to tell you you're wrong, here, but I am going to expound upon the truth a little bit. The above image of raw sienna and yellow ochre is about how I picture them in my head, too– sienna being slightly on the cool, green side, ochre being warmer and more luminous. Here, the pigment index number raw sienna is PY43 and yellow ochre is PY42, so we can see that they are different pigments. PY stands for "Pigment Yellow" and then the number that follows is just based on the order the pigments were added into the Colour Index International (CII) originally published in 1925, which has no correlation to when the pigments were founded. Artists pigments (and dyes) are coded in this manner so we can have chemical clarity on what is in our paint, since the name on the tube can have as little or as much relation to the pigments inside as the manufacturer desires. I have put together a chart examining the iron oxide paints made by Williamsburg Handmade Oil colors. This is not an exhaustive list of iron oxide paints, but it is an exhaustive list of those made by Williamsburg (to my knowledge). I chose to examine only single pigment paints. No blends, for clarity's sake. Williamsburg makes twenty different paints that contain PY42, and only three of those twenty paints contained PY42 alone. Based this criteria, there were three paints that I cut from the PY43 list, eight paints I took off the PR101 list (Pigment Red), two paints from PR102, and six paints that got the boot from PBr7 (Pigment Brown). Notice the immense overlap in some of the nomenclature surrounding these pigments. You can see that many colors we think of as different, like our ochre and sienna from before, may not be so different after all. For a look at these stunning colors, check out Williamsburg's website for some sharp draw out reproductions.
I am an Artist Educator on behalf of Golden Artist Colors which extends to Williamsburg and QoR. GOLDEN acquired Williamsburg in 2009 after the passing of Williamsburg's founder, Carl Plansky. Although I am trained to teach about the company's products, I designed this chart based off my own independent research which was in no way sponsored or approved by Williamsburg.
All this to say: wow. The versatility, range, and variation within these tried and true pigments is insane. Students often come to me in total confusion after they notice that our burnt sienna, burnt umber, and raw umber Guerra pigment dispersions are all listed as PBr7. How can these colors all be the same thing? The actual hue and behavior of an iron oxide can vary immensely based on where it is obtained from, how it is (or isn't) processed after the fact, and whether or not it's synthetic. Both natural and synthetic iron oxides can be calcined, where they are heated to extremely high temperatures (at least 300°C/572°F) for a duration of time. Hence, "burnt" sienna. Hence, three noticeably different colors with the same index number. It's here that the romantic idea of digging up the earth and grinding it into paint begins to morph into the dark arts. Different chemicals, metals, or minerals can be added into the calcination process to alter the hue. Synthetic iron oxides, such as Mars pigments, are based on either thermal decomposition of iron compounds or aqueous precipitation from solutions of iron salts (Berrie 72). Gamblin Artist's Oil Colors has marketed a specific line of "transparent" earth colors where the synthetic iron oxide molecule (i.e. Mars) has been hydrated to achieve transparency. The process of hydration is also used to turn chromium oxide green into viridian. Interestingly enough, the particle shape and size of earth pigments is critical to determining opacity, and can be adjusted by manufacturers to yield an extremely transparent pigment without actually pushing the material through further chemical processes or hydration. While a lot of the synthetic stuff is cool, perhaps we overlook the natural capabilities of these modest colors.
Gamblin's Earths– check out the three hydrated synthetic iron oxides on the bottom
Earth pigments aren't exactly modern technology. We're talking Paleolithic stuff, here. Because of their stability and relative opacity, earth pigments have always been used for grisaille and underpainting. Literally the first iteration of paint that we know of is still the foundation of painting as we know it. I've heard some flak towards iron oxides tossed around amongst painters, with complaints that they're lifelessly opaque and lacking vibrancy. They are familiar and accessible, therefore painters don't seem interested in unearthing their many nuances. Rather, painters seem to gravitate towards newer, cooler, brighter, bolder color solutions. I implore painters to dig deeper. While I totally embrace the developments in color technology and believe it's every artist's responsibility to endlessly push forward, earth pigments are timeless. Timelessness in that they actually hold up to the test of time, and timeless in that they always have been and always will be essential for artists. With pigments as strong as iron and as unwavering as the steadfast cliffs and quarries whence they came, let our minds and palettes be grounded by the earthly link these colors provide between ourselves and the centuries of artists that have come before us.
And with that, let the chaos continue.
Lascaux Cave murals in the Southwest of France containing natural earth pigments – estimated creation date 17,000 B.C.