What Is Ochre?: Earth Pigments Explained
This is a question we are asked with unvarying frequency. Ochre pigments are one of the most plentiful natural pigments, encompass a rather diverse range of colors, and have been in popular use since long before it occurred to humans to record their history. However, while Ochre pigments have been in constant use for literally hundreds of thousands of years and are still widely popular today, many artists still struggle to define just what exactly Ochre is…
Ochre & Earth Pigments: French Red Ochre, French Orange Ochre, Italian Yellow Ochre, Italian Green Earth, Australian Vivianite, Armenian Purple Ochre, Italian Brown Earth, Russian Shungite
What is Ochre?
Ochre is a type of earth pigment that primarily derives its color from iron oxide, while also including an assortment of other accessory minerals, as well as salts and clays, all of which influence the ultimate color of the pigment.
Ochre pigments are inorganic (meaning mineral-based), and are widley considered to be some of the most permanent pigments in existence. (This can be confusing due to to the modern use of the word 'organic' to mean naturally occurring. 'Organic' technically refers to the situation of a substance being carbon-based. Organic pigments (meaning animal and vegetable-based) are generally not lightfast, with the obvious exception being modern synthetic organic pigments, such as the Quinacridones.)
Ochres are formed secondarily in iron-rich soils and as iron ore deposits decay, which can partially explain why they are generally relatively soft and easy to process into pigments. This quality, along with their accessibility and widespread prevalence, are what has made them one of the most used pigments in history.
Cave paintings at Lascaux site, France. These were created using various iron oxide pigments.
So... What is Iron Oxide?
Iron oxide, commonly known as rust, is the mineral substance that so generously imparts to Ochres their distinctive colors. It occurs naturally everywhere on Earth in various forms, of which are responsible for determining different colors. Rocks that contain higher percentages of iron oxide are more deeply colored, while those that contain only trace amounts are nearly colorless (such as white clays and limestone).
While the different forms of iron oxides can occur together in various combinations, the mineral occurring in greatest dominance determines the overall color of a pigment sample, though that color is of course influenced in varying degrees by the other forms of iron oxide present, various accessory minerals, and the overall composition of the sample.
The Main Types of Iron Oxides & Their Colors
Greenleaf & Blueberry Armenian Hematite (unreleased), Cypriot Limonite, and Norwegian Magnetite.
Red - Hematite: Iron Oxide (Non-Hydrous) Fe2O3
Anhydrous ferric oxide
Greenleaf & Blueberry French Red Ochre Watercolor, demonstrated in a Gravity Wash
Hematite is an anhydrous ferric oxide, and imparts a red color. It is considered to be the pure mineral form of iron oxide. Hematite is from the Greek work hema, meaning blood, referencing the red color of the mineral.
Yellow - Goethite: Iron(III) Oxide-Hydroxide (Hydrous) FeHO₂
Greenleaf & Blueberry Cypriot Limonite Watercolor, demonstrated in a Gravity Wash
Limonite, a hydrous ferric oxide, is generally considered to be responsible for the yellow coloration seen in many Ochres. However, Limonite refers to a matrix base made of other minerals. It is not considered a true mineral because it does not have a specific chemical formula or crystalline structure. Goethite (and less commonly lepidocrocite) is the predominant mineral in Limonite, responsible for both its recognizable yellow color and its predominant characteristics.
Black - Magnetite: Black Iron Oxide Fe2+Fe3+2O4
Iron (II,III) oxide or Ferrous-ferric oxide
Greenleaf & Blueberry Norwegian Magnetite, demonstrated in a Gravity Wash
Magnetite, as you might surmise, is a strongly magnetic pigment. It is an iron ore containing equal amounts of ferrous iron and ferric iron, less popularly called ferrous-ferric oxide. (Ferrous is divalent and ferric is trivalent. An element's valency is a measure of its capacity to combine with other atoms when forming new molecules or chemical compounds). Magnetite is black or nearly black in color, and so is responsible for the darker Ochres.
Ochre vs. Earth Pigment
When it comes to Ochre and Earth pigments, their mineral components, and their history, it is difficult to draw clear, definitive lines when sorting pigments into these different categories. Artists and scientists may use different terms, and the art supply industry's chaotic use of archaic, descriptive, or whimsical names only adds to the confusion.
Generally, the term 'earth pigments' refers to easily accessible and readily processable pigments that can be dug from the earth. Ochres are a category of earth pigments, united by receiving their color primarily from different iron oxides, and encompassing a range of reds, yellows, browns, and blacks.
Green Earths (also known as terre verte) are called 'earths' and not 'ochres' because they receive their coloration not from iron oxides, but from iron silicates (generally glauconite and celadonite). We will get into those another time (however, in the mean time I invite you to read my ode to Green Earth here).
What Ochre Pigment Is Made Of
Now that we understand from where ochre pigments receive their color, let's get into what ochre pigments really are - what they are made of.
Components of Ochre Pigment:
Primary Component: This component is the dominant color-producing agent, such as hematite, goethite, or magnetite.
Secondary Component: This component is the secondary or modifying coloring agent. This might include hematite, goethite, magnetite, or an array of other minerals. This component influences the overall color (and behavior) of the sample, but is of a smaller percentage than the primary component.
Base Component: This component is the base or carrier of the color, and is most commonly made of some sort of clay. The composition of clays varies widely. (What is clay? In a nutshell: clay usually forms from the chemical weathering of silicate rocks. The type of clay that is formed depends on the source rock and the weathering conditions, such as acid vs. alkaline.) Clays are often light in color (darker colored clays usually receive their color from small quantities of our good friend iron oxide), and therefore they often act as a kind of diluent to the pigment sample. As a result of the base clay component, the overall color of the pigment is generally lightened, made more transparent or opaque, etc.
American Red Ochre Sample
Because of the varieties of factors in each component, you can easily see why Ochre samples from different locations vary so greatly and confound efforts to conveniently categorize them by color or behavior. It is not just the geology that effects a sample, but the climactic conditions that have acted upon it over time, and the resulting chemistry in how these materials interact that determine the final result that arrives on the artist's palette.
In this way, each Ochre pigment sample, like wine, has a kind of terrior, a unique color and set of handling characteristics determined by its source and history.
A Red Ochre from Morocco will be different from a Red Ochre from France will be different from a Red Ochre from America. Each source is different, and even each layer within a source is different. To call a paint simply 'Red Ochre' is the tip of the iceberg at best, and leaves out an essential piece of information for the artist - which Red Ochre. The connection to place isn't just interesting information, it should be considered essential knowledge for painters.
The famous Roussillon Ochre Cliffs in France, historically considered the source of the very finest red Ochres.
Let's Talk about Sienna & Umber...
Raw Sienna, Burnt Sienna, Raw Umber, and Burnt Umber are very commonly found in most color lines, and on most palettes. If you have only a narrow experience in painting of any medium, these color names are probably familiar to you. But, like, what are they?
I took the trouble above to denote the different chemical variations of the different iron oxides - not to dazzle you with detailed chemical and geological facts, or put you to sleep for an afternoon nap (if I already have, pleasant dreams!); I shared that because it is necessary information to really understand some of the most widely used pigments on the painter's palette: the Siennas and Umbers.
Raw Sienna and Raw Umber are generally Goethite-based Ochre pigments, meaning they are hydrous iron oxides, meaning that good old H2O (water) is part of their chemical composition. You may have surmised from the terms 'raw' and 'burnt' that a transformation of sorts is involved with these pigments. Indeed, when you calcine (fire or roast) Raw Sienna and Raw Umber, the heat causes them to undergo a chemical change that results in their colors changing. This is because the process of calcining (again, heating) effectively burns away the water, thereby converting goethite (hydrous iron oxide) into hematite (non-hydrous iron oxide), explaining the darker, warmer, redder tones of Burnt Sienna and Burnt Umber.
What is the difference between Sienna and Umber?
Besides their historical place of origin, Sienna receives it's yellow from a high concentration of Goethite, while Umber also contains manganese oxide, which expresses a range of browns, dark browns, and blacks.
Now, the original, defining source of the finest Siennas was Siena, Italy. However, that source has long been depleted. Natural Siennas now often come from Sardinia and Sicily, yet the name has remained the same...
Names of Ochre Pigments
There are many Ochre pigments that do not include the word 'Ochre' in their names because they still bear remnants of their history and original source. In many instances, such as the case with Sienna, the name remains but the original source does not - making things just a little more befuddling...
Below I will list some common paint colors that fit into the Ochre category, explain how they fit in with what I have explained above, and demystify their names a bit.
Sinopia - A red iron oxide pigment sourced from the town of Sinop, Turkey on the coast of the Black Sea, beginning in classical antiquity. The pigment from this specific source was so valuable to ancient Greece and Rome that it was sold stamped with a special seal to differentiate it from possible substitution, and was called "sealed Sinope". In the middle ages, this name came to refer to a range of red ochres, and was popular in the 15th century especially. It became recognized for its use as an underdrawing, which became known as the 'sinopia'.
Location of the town of Sinope on a current day map.
Indian Red - Originally imported from the East Indies, it is recognized today as a darker red color with a blueish undertone.
Venetian Red - While the origin story of this pigment has been obscured by time, today there are still sources of red ochre outside of Venice. Venetian Red is now generally denotes a brighter form of red ochre. This may be due to the Venetian source containing gypsum, a white mineral, as a base component.
Caput Mortuum - The literal and somewhat alarming Latin translation is "death's head" or "worthless remains", which would lead you to assume this pigment dates from Roman times, however this term was bestowed upon it by seventeenth century alchemists as a way to refer to unusable leftover residue from experiments (early synthetic iron oxides, most likely), and was only used to refer to a pigment in the eighteenth century. This term generally refers to synthetic deep brown-purple iron oxides.
Pozzuoli Red - Also called Terra Rosa, it is a warm, clear brown-red pigment originally sourced from Pozzuoli, Italy near Naples. It was very popular for use in frescoes during the Renaissance.
All that really remains of many historical pigments in today's paints is the hue and the name, while the pigment has changed - sometimes to a different source, sometimes to a completely different (often synthetic) pigment or even a combination of pigments used to approximate the original hue.
Why New Names For Ochres Are Important
From left to right: American Pipestone (Catlinite), French Red Ochre, Moroccan Red Ochre, French Red Ochre Dark, Icelandic Red Earth
Having a connection to our art supplies helps us understand how to more purposefully use them. The paint industry has gotten rather carried away with whimsy and unnecessarily romanticizes the past as a way to sell colors. Additionally, many fine art schools do not place any kind of meaningful emphasis on materials, instead focusing more heavily on subject and concept.
One company's Venetian Red may contain entirely different pigments from the next. One may be a mix of pigments, another may be synthetic, and another may be natural but not from Venice or even Italy. The only unifying feature across different lines might be a roughly similar hue, which in painting means rather little.
Further, the color index labels all chemically similar pigments with the same code, so there is no differentiation between natural sources, even through pigments from different mines can vary widely in both color and characteristics.
I believe you should be able to understand what pigment is in your tube and where it came from. You will not only begin to distinguish between as well as understand what to expect from pigments from different regions, but you may find you are developing preference of provenance for certain types of pigments. This is why we list country of origin for all of our naturally occurring pigments, and it is why all of our colors are single pigment paints.
Synthetic Ochres... And How To Spot Them
Iron oxides have been synthesized since at least the eighteenth century when they were given the brand name of 'Mars'. They generally have a stronger tinting strength, are brighter in color, and have more opacity compared to the natural variety. Many artists will notice the difference between working with natural versus synthetic iron oxide pigments.
There is some speculation as the source of the name Mars, but it likely comes via circuitous route from the Roman god of war and agricultural guardian Mars, whose metal just happens to be: iron. He was ceremonially called upon to drive away rust (iron oxide), which would be especially appreciated by those who wield either weapons or farm implements.
There are two main ways to distinguish natural and synthetic iron oxides: name and pigment index number.
Name - If the the color name contains Mars, then it contains a synthetic iron oxide pigment. Caput Mortuum also generally refers to a synthetic pigment. However, just because the color name does not contain these terms does not mean it does not contain synthetic pigments.
Color Index Number - The color index assigns a basic code to different types of pigments. With all the confusion of naming, this is a very helpful system. However, it falls short in that it lumps pigments from different natural sources together, as well as failing to distinguish between synthetic pigments from different manufacturers together as well. However, any reputable paint company will list the pigment index codes on their paint labels so that customers can understand (at least generally) which pigments they are using. Natural iron oxides and synthetic iron oxide have different pigment index numbers.
Understanding Color Index Codes:
P = Pigment, the first letter in the code
Second letter in the code denotes color category of the pigment.
R = Red, O = Orange, Y = Yellow, G = Green, B = Blue, V = Violet, Br = Brown, Bk = Black, W = White
# = specific pigment within color category
PR102: Natural iron oxide: red category.
PY43: Natural iron oxide: yellow category.
PBr7: Natural iron oxide: brown category.
PR10: Synthetic iron oxide: red category.
PY42: Synthetic iron oxide: yellow category.
PBr6: Synthetic iron oxide: brown category.
Just flip over your paint tube or check your pan wrapper to see which code is listed and you will be able to tell if your color is natural or synthetic.
Wait, What About Vivianite (Blue Ochre) & Purple Ochre?
Purple Ochre receives its color mainly from iron oxide, however its secondary component is a high percentage of silica - not quite so high as to be the primary component, but high enough to significantly influence the color.
Vivianite is an iron phosphate. To be brief: iron oxide is based around the element oxygen, where an iron phosphate is based on phosphorus. There is much more that can be said about it, however I will save that for another day. Technically, Vivianite is not a true Ochre, though there are strong enough similarities and chemical relationships, and categorizations loose enough, that it is a fringe part of the Ochre family.
Why Ochre Pigments Belong On The Watercolorist's Palette
Natural Ochres are widely available, and generally inexpensive compared to other pigments. Additionally, and more significantly, they are beautiful pigments. Today they are often drowned out by the louder voices of the high chroma modern synthetic pigments. By comparison they can look rather dull and drab. However, as the softest voices are often the ones most worth listening to, so too the more subtle colors can also be the most interesting.
Ochre and earth colors sing most sweetly when used together - they have a kind of harmony this way. Now that you understand what Ochre and Earth pigments are, this is probably unsurprising to you!
Quick sketch of a robin painted using only Ochre & Earth colors: French Red Ochre, French Orange Ochre, Italian Yellow Ochre, Italian Green Earth, Australian Vivianite, Italian Brown Ochre, Russian Shungite
To make Ochres sing in your paintings, I suggest an all Earth/Ochre or greyed-down tones. In the absence of punchy high chroma colors, these pigments will shine forth. They can also be used as a mixing base and subtly augmented by small amounts of higher chroma colors to dial up the volume here and there, or to more precisely match colors.
Indeed, Ochres are responsible for the soft translucent skin tones of paintings by the Old Masters. Intense colors can often be more than is needed and leave you mixing colors till you go mad. Remember that less is more and enough is as good as a feast. Ochre pigments embody this and are deserving of a place at the table - and in the artist's palette.
Ochres are a somewhat capacious rather sprawling topic. I have tried to distill down and present to you the information that I find most illuminating and necessary to understanding what an Ochre pigment really is, and sharing what is relevant to the painter. I hope you found it useful! Please leave any lingering questions in the comments below and I will do my best to answer them.
As always, wishing you happy painting!