How Pigments Create Color In Paintings

A pigment shows you a color because its atomic structure absorbs some wavelengths of light and reflects the rest back at your eye. That single mechanism, selective absorption, explains why a Renaissance ultramarine blue once cost more than its weight in gold, why a Berlin dye-maker's failed red experiment in 1704 gave the world an entirely new blue, and why some of the most famous paintings on Earth are quietly rotting from the inside because of pigments artists trusted for centuries. The chemistry is simple. The history built on top of it is not.

Absorption, not addition, is the actual mechanism

White light from the sun or a studio lamp is a mixture of every visible wavelength, roughly 380 to 700 nanometers, running from violet through blue, green, yellow, orange, and red. When that light hits a pigment particle, the electrons in its molecular or crystal structure absorb certain wavelengths and convert that energy into heat, while the wavelengths they can't absorb bounce back off the surface or scatter through the paint layer. What reaches your eye is only the reflected remainder, and your visual system interprets that remainder as the pigment's color.

A red pigment, for instance, absorbs most of the blue and green portion of the spectrum and reflects predominantly long wavelengths in the red range. It isn't adding red to the light falling on it. It's subtracting nearly everything else and letting red pass through unabsorbed. This is a subtractive process, and it behaves completely differently from how a television or phone screen produces color, where red, green, and blue light are combined additively and stack toward white.

That distinction is why mixing paint and mixing light produce opposite results. Combine two pigments and you combine their absorption properties: each pigment keeps absorbing the wavelengths it always absorbed, so the mixture removes more of the spectrum than either pigment did alone, and the result trends darker and more muted. Combine two beams of colored light and you're adding wavelengths together, which trends the result toward white. A painter mixing blue and yellow paint gets a duller green because the mixture absorbs more of the spectrum than either color did on its own; a lighting designer overlapping blue and yellow spotlights gets something closer to white, because the light sources are adding photons rather than subtracting them.

The color you see in a pigment is, physically speaking, the light the pigment rejected. Every wavelength that actually reaches your retina from a red paint chip is a wavelength the paint's molecular structure failed to absorb.

Why does mixing paint colors darken while mixing colored light lightens them?

Paint mixing is subtractive: each pigment removes wavelengths from the light hitting it, so combining pigments removes more of the spectrum and darkens the result. Light mixing is additive: combining light sources adds wavelengths together and moves toward white, the opposite direction entirely.

Ultramarine: chemistry meeting geology and economics

Natural ultramarine comes from grinding lapis lazuli, a semi-precious metamorphic rock whose deep blue comes from a sulfur-containing mineral called lazurite embedded in a matrix of calcite and pyrite. For most of the medieval and Renaissance periods, the only significant known source of gem-quality lapis lazuli was a set of mines in the Sar-e-Sang valley of what is now Badakhshan province in Afghanistan, a region that had already been supplying lapis to Mesopotamia and Egypt for thousands of years before it reached European painters. Getting the stone out of that mountainous region and across trade routes to Venice, Florence, or Bruges added enormous cost before a painter ever touched it.

Extracting usable pigment from the raw stone was its own ordeal. Crude grinding just produces a grayish powder contaminated with the calcite and pyrite locked into the rock; a genuinely vivid blue required a laborious purification process, developed and refined over centuries, in which ground lapis was kneaded into a resinous, wax-and-oil dough and repeatedly worked in a dilute lye solution so the blue lazurite particles would separate out from the duller mineral impurities and settle at the bottom. The first extractions from a given batch of lapis produced the purest, most expensive blue; later, weaker extractions from the same batch were sold more cheaply as "ultramarine ash," a visibly grayer product used for less important passages of a painting.

This combination of a single distant source and a punishing purification process made ultramarine one of the most expensive materials a Renaissance workshop could buy, regularly compared to gold by weight in period accounts and contracts. Painters and patrons responded by treating the pigment as a deliberate signal of status and devotion rather than an ordinary studio supply. Commission contracts from the period sometimes specified, in writing, how much ultramarine the painter was required to use and on which figures, with the Virgin Mary's robes a recurring reason to justify the expense, since blue drapery rendered in true ultramarine communicated the sitter's or patron's seriousness of investment as clearly as gold leaf did.

Pigment	Source material	Era of primary use	Key hazard or instability
Ultramarine (natural)	Lazurite from lapis lazuli, mined in the Sar-e-Sang valley, Afghanistan	Medieval period through the Renaissance	Not toxic, but scarcity made it cost-prohibitive for all but the wealthiest commissions
Vermilion (cinnabar)	Mercury sulfide (HgS), ground from the mineral cinnabar or synthesized	Ancient world through the 19th century	Toxic mercury content; the pigment itself can darken to gray or black under light exposure
Lead white (flake white)	Basic lead carbonate, produced by corroding lead metal with vinegar fumes	Ancient world through the mid-20th century	Severe lead toxicity to painters through inhalation, skin contact, and brush-licking habits
Prussian blue	Synthetic iron ferrocyanide, discovered accidentally in Berlin around 1704	1720s onward	Chemically stable and low-toxicity relative to older blues, though it can fade under intense, prolonged light
Cadmium yellow	Cadmium sulfide (CdS), first proposed as a pigment in 1819	Mid-19th century onward	Cadmium compounds are toxic if inhaled as dust; the set pigment particle itself is comparatively low-risk when bound in paint

Five pigments that map the trade-off painters have always navigated: color intensity and permanence against cost, availability, and personal risk.

The 1704 accident that broke ultramarine's monopoly

Ultramarine's centuries-long dominance as the only truly vivid, stable blue ended not through a deliberate research program but through a failed attempt to make red paint. Around 1704, in Berlin, a color-maker named Johann Jacob Diesbach was trying to prepare a red lake pigment using cochineal insects while working in the laboratory of the alchemist Johann Konrad Dippel. He needed potash, an alkaline material, to complete the process and used a batch that had been contaminated during an earlier procedure involving animal blood and oil in Dippel's workshop.

Instead of the red he expected, the mixture turned a deep, saturated blue. The contaminated potash had reacted with the animal-derived material to form potassium ferrocyanide, and when that combined with the iron sulfate in Diesbach's recipe, it produced iron ferrocyanide, the compound now known as Prussian blue. It is generally credited as the first modern synthetic pigment, a color made deliberately reproducible through a chemical process rather than mined and physically purified from a mineral like lapis lazuli.

Prussian blue reached the commercial art-supply market by the 1720s and spread across Europe within a few decades, in large part because it undercut natural ultramarine dramatically on price while still offering a strong, workable blue. It never fully displaced ultramarine, since true ultramarine's particular hue and stability under most conditions kept it valuable for specific uses, but Prussian blue gave painters outside the wealthiest patronage circles their first genuinely affordable deep blue, and it went on to become a defining color in works as far-flung as Katsushika Hokusai's woodblock prints in Japan in the following century.

When did synthetic ultramarine finally arrive?

Natural ultramarine's cost advantage over synthetic blue rivals lasted until 1826, when the French chemist Jean-Baptiste Guimet won a government-sponsored prize for producing an artificial ultramarine with the same core chemical structure as the natural pigment. Within a few decades, the synthetic version made ultramarine-quality blue affordable for ordinary painting supplies for the first time in the pigment's history.

Toxic pigments painters used for centuries anyway

Two of history's most heavily used pigments carried serious, well-documented health risks that painters largely accepted, tolerated, or simply didn't fully understand for centuries. Lead white, also called flake white, is a basic lead carbonate produced historically by suspending coiled sheets of lead metal over vinegar inside sealed containers, then stacking those containers above fermenting horse manure, whose warmth and carbon dioxide output helped convert the corroding lead surface into flakes of pigment that were then scraped off, ground, and washed. It produced an opaque, warm, workable white that dominated Western painting from antiquity into the twentieth century, and there was effectively no equally good substitute until modern titanium white pigments matured.

The cost was chronic lead exposure. Painters ground the pigment by hand, inhaled dust during preparation, absorbed lead through skin contact, and, in a habit conservators and historians have documented repeatedly, often shaped a fine brush point by licking the bristles, swallowing lead-laced paint directly in the process. Symptoms of chronic lead poisoning, including abdominal pain, fatigue, joint pain, and neurological problems, were common enough among painters and tradespeople that the nineteenth century coined the term "painter's colic" for the chronic constipation lead poisoning produces. Lead white pigment was not banned across the European Union until 1992, a regulatory gap of well over a century after its dangers were understood in general terms.

Vermilion, the traditional brilliant red made by grinding the mineral cinnabar or synthesizing an equivalent mercury sulfide compound, carried a different pair of risks: acute mercury toxicity to the people producing and handling it, and a documented tendency for the finished paint layer to darken over time. Research using Raman spectroscopy and other analytical techniques has traced this darkening to multiple interacting chemical processes, including light-driven transformation of the red hexagonal crystal form of mercury sulfide into a black cubic form called metacinnabar, and photo-induced formation of metallic mercury within the paint film, sometimes assisted by trace chlorine compounds. That means some passages of red in centuries-old paintings that now read as gray or blackish were originally a bright vermilion red, a fact conservators account for when interpreting how a painting's palette has drifted from the artist's original intent.

Lead white pigment, used continuously in Western oil painting from antiquity through the mid-twentieth century, was not banned in the European Union until 1992, meaning the regulatory response to its documented toxicity trailed its introduction by well over a thousand years.

Different eras, different available chemistry

The palette available to a painter in any given century was constrained by what mineral sources, synthesis methods, and trade routes actually existed at the time, not by artistic imagination. Vivid, lightfast greens were a persistent problem before modern industrial chemistry: historical green pigments were often copper-based compounds, such as verdigris, that are chemically unstable and shift toward brown or black as they age through reaction with the surrounding paint medium and atmosphere, which is one documented reason some historical paintings show muddier or more brownish greens today than the artist originally applied.

The nineteenth century changed the equation dramatically. Between Guimet's 1826 synthetic ultramarine and a wave of new pigments developed through industrial chemistry, including cadmium-based colors, painters gained access to a far broader and more reliably stable palette than any prior generation. Cadmium was identified as an element in 1817 by the German chemist Friedrich Stromeyer, who recognized cadmium sulfide's potential as a yellow pigment almost immediately, though it did not reach commercial availability until the 1840s because of how scarce the metal was to extract from zinc ores at the time. Cadmium yellow, along with related cadmium reds and oranges developed later in the century, gave painters an intense, opaque, and comparatively stable warm color range that natural mineral and organic sources had never reliably supplied.

This is also the century that gave Impressionist and Post-Impressionist painters much of their signature vividness. Portable metal paint tubes, invented in the 1840s, combined with this expanding range of chemically synthesized, factory-produced pigments to let painters carry saturated, stable colors outdoors for the first time, a practical and chemical shift that reshaped how landscape painting itself was practiced.

A common misconception: pigment and dye are the same thing

Pigments and dyes get used interchangeably in casual conversation, but the chemical distinction between them mattered enormously to painters and still matters to conservators today. A pigment is an insoluble particle that has to be physically suspended in a binder, whether linseed oil, egg yolk for tempera, or an acrylic polymer emulsion, to be applied and held in place on a surface. A dye, by contrast, is soluble and chemically bonds to or is absorbed directly into the material it colors, the way a textile dye penetrates and stains fabric fibers at a molecular level rather than sitting on top of them as discrete particles.

That structural difference explains why pigments generally resist fading from light exposure, a property conservators call lightfastness, better than dyes do. A pigment particle's color comes from a stable crystal or molecular structure that is physically embedded within the paint film; light has to actually break down that crystal structure to change the color, which many mineral pigments strongly resist. Many dyes, by comparison, are more chemically exposed and prone to photochemical breakdown, meaning ultraviolet and visible light can trigger reactions that degrade the color-producing structure relatively quickly.

This distinction created a specific, well-documented historical problem. Painters have long used organic lake pigments, made by chemically precipitating a soluble dye, often derived from insects, plant roots, or other organic sources, onto an inert, insoluble base material like alumina, which converts the soluble dye into something that behaves and can be applied like a pigment. But that conversion doesn't erase the dye's underlying chemical vulnerability, so lake pigments inherited much of the poor lightfastness of the original dye. This is a documented reason certain reds and purples in older paintings have faded, shifted hue, or disappeared almost entirely over the centuries, sometimes dramatically more than the mineral-based pigments used right alongside them in the same painting.

Why do some old paintings look faded or discolored compared to when they were made?

Some pigments used historically, particularly organic lake pigments made from unstable dyes and certain copper-based greens, are chemically prone to fading or color shift under light and atmospheric exposure over centuries. Conservators account for this when analyzing a painting's original palette, since the colors visible today aren't always the colors the artist actually applied.

Modern pigment chemistry, developed and standardized through the twentieth century, built lightfastness testing directly into how new pigments are evaluated before commercial release, specifically to avoid repeating this recurring historical failure. Contemporary painters working today have access to color options with documented, tested permanence ratings that simply didn't exist for painters working even a century ago, let alone during the Renaissance.

What conservators actually do with this chemistry

Understanding pigment chemistry isn't only useful for explaining why old paintings look the way they do today. It is the working foundation of art conservation and authentication, fields that rely heavily on identifying exactly which pigments are present in a given paint layer. Techniques like X-ray fluorescence spectroscopy and Raman spectroscopy let conservators identify a pigment's elemental or molecular fingerprint without removing a physical sample, which matters enormously when the object under study is an irreplaceable painting.

Because different pigments came into commercial use at documented points in history, like cadmium yellow's arrival in the 1840s or titanium white's later development in the twentieth century, finding a pigment in a painting that wasn't chemically available until after the artwork's claimed date is one of the more reliable tools conservators and forensic art historians have for flagging forgeries or misattributed works. A painting attributed to a sixteenth-century workshop that turns out to contain a pigment first synthesized in 1826 has a serious dating problem, regardless of how convincingly the brushwork imitates the period style. This same underlying chemistry, understood through techniques like ultraviolet fluorescence imaging, also helps conservators distinguish an artist's original paint layer from later retouching or restoration work added by someone else entirely.

The takeaway

A pigment's color is fundamentally a chemistry problem: it comes down to which wavelengths of light the pigment's molecular or crystal structure absorbs and which it reflects back to your eye. But which pigments were actually available to a painter working in a given century was never purely a chemistry question. It was a geology problem, decided by where a usable mineral could be mined; a trade problem, decided by how far that mineral had to travel and at what cost; and, eventually, an industrial chemistry problem, decided by which synthesis processes chemists had figured out how to scale. Ultramarine's path from a single Afghan mountain valley to a cheap, mass-producible synthetic blue in the nineteenth century, running directly alongside vermilion's mercury risk, lead white's toxic legacy, and Prussian blue's accidental Berlin origin, shows that the history of color in painting has never really been separable from the history of chemistry, geology, and trade.

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Read next:

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FAQ

Q: Why does mixing paint colors darken them, while mixing colored light lightens them?

Pigments work by absorbing wavelengths, so combining pigments combines their absorption properties, generally removing more of the light spectrum and producing a darker result. Colored light mixing is additive, combining wavelengths together, which moves toward white rather than black.

Q: Why was ultramarine blue historically so expensive?

It was made from lapis lazuli, a semi-precious stone whose primary known source for centuries was the Sar-e-Sang valley in present-day Afghanistan, combined with a laborious extraction and purification process, making the pigment cost comparable to gold by weight during the Renaissance.

Q: When did synthetic ultramarine become available?

French chemist Jean-Baptiste Guimet synthesized an artificial version with the same chemical structure as natural ultramarine in 1826, winning a government prize for the achievement and eventually making the pigment far more affordable than its natural mineral source.

Q: Do all historical pigments keep their original color over time?

No. Some historical pigments, including certain copper-based greens and vermilion, are chemically unstable and shift color as they age, which is one reason paintings can look different today than when they were originally created, and a factor conservators account for during restoration analysis.

Q: How was Prussian blue discovered?

A Berlin color-maker named Johann Jacob Diesbach accidentally created it around 1704 while trying to make a red pigment using contaminated potash. The contamination produced iron ferrocyanide instead, a stable synthetic blue that became commercially available by the 1720s and undercut natural ultramarine's price dramatically.

Q: What is the difference between a pigment and a dye?

A pigment is an insoluble particle suspended in a binder like oil or acrylic to be applied to a surface, while a dye is soluble and chemically bonds into the material it colors, such as fabric fibers. This difference is a major reason pigments generally resist fading better than dyes.

Q: Were any historical pigments actually dangerous to the painters who used them?

Yes. Lead white, used continuously from antiquity into the twentieth century, caused documented chronic lead poisoning in painters through inhalation, skin contact, and brush-licking habits, and wasn't banned in the European Union until 1992. Vermilion's mercury sulfide content posed similar risks to the people producing and handling it.