Mulling it Over: Contemporary Pigment Grinding

The founder and owner of Tri-Art, Steve Ginsberg, often reminds us that paint is the raw material of an artwork – an artist must endeavour to transform paint into a finished piece. Just as paint by itself does not make a painting, pigments do not simply make paint – the manufacture of paint requires the careful manipulation of raw ingredients and techniques to produce not only paint, but high-quality artists’ paint. Pigment grinding is the essential step that allows powdered pigments to be transformed into smooth, liquid paint. The process is in itself an art form that receives little attention, even in the world of artists’ supplies. While pigment load is often given primacy over all else when evaluating paint, the quality of the pigment’s dispersion is just as critical when bringing out the best in each pigment.

Aggregating Data: A Brief Primer on Grinding Pigments

While pigments appear to be fine powders composed of evenly ground particles, these particles clump together on a very small-scale forming aggregates. These clumped together particles can have significant effects on the final appearance of the paint: they can appear as physical gritty particles, lower the colour intensity (chroma) of the paint, and effect the opacity or transparency of the paint. Clumped particles can lower the opacity of an opaque colour, or confusingly lower the transparency of a transparent colour. When aiming for opacity, dispersing these particles is critical to attainting maximum covering powering. When it comes to transparent colours, these aggregated particles of pigment can also trap pockets of internal air that scatter light.[1] Rather than allowing light to pass through, these air pockets create paint that looks hazy, like frosted glass. Therefore, one of the primary functions of pigment grinding, as suggested by the name, is to break apart these aggregates to create an even dispersion.

Paint outs of Pyrrole Red acrylic Figure 1: Pyrrole Red. Left, poorly dispersed pigment shows a lack of transparency. Left, the well ground pigment has an excellent transparency and full depth of colour.

The traditional techniques of grinding pigment have gone unchanged for centuries. Handmade paint using a muller and glass slab is making a resurgence today. With gentle circles of the muller, the pigment is dispersed into a medium, like gum Arabic for watercolour or linseed oil for oil paints. The action of the muller against the glass shears apart the aggregated pigment particles and replaces any air with the binder of choice.

a glass muller with red pigment and a palette knife. An etching from 1751 showing a grinding stone muller with pigments.

Figure 2: Left, a modern glass muller. Right, a detail from the 1751 Encyclopedia of Diderot & d’Alembert showing the same. “Plate VI: Painting, Folding Easel and Traditional Easel, Pastel Box and Grinding Stone”. Image via The Encyclopedia of Diderot & d’Alembert Collaborative Translation Project. Ann Arbor: Michigan Publishing, University of Michigan Library, 2010. Web. [January 19, 2021]. <

Acrylics: Modern and Mullers Don’t Mix

Despite a Renaissance of handmade paint, nearly all artists today buy their paint pre-made, and for good reasons. Working with dry, powdered pigments alone is health hazard, and quite a messy undertaking. When it comes to making acrylics, the process is even more difficult. Ignoring the complex formulation and stepwise process necessary to create acrylic paint from its raw materials, if you wanted to mix a pre-made acrylic medium with pigment you would find the results might not be what you hoped.  Acrylic emulsion paints cannot truly be mulled by hand like oil or watercolour because they rapidly dry and are not resoluble. Mixing a paint from pigment takes considerable time, the paint must be carefully mulled, tested, and mulled further, often with adjusting the amount of pigment or binder added. This is time that acrylic paint does not allow for.

Acrylic paints are really only possible thanks to the industrial and chemical advances of the 19th century and the post-war era. By the 19th century, oil paints were not being made just by hand with mullers. Mechanical, large-scale, roller mills were developed for commercial artists paint production. These allowed for larger volumes of paint to be produced, with more evenly dispersed pigments than could be produced by hand. With the invention of the metal paint tube in 1841, most artists would buy their paints pre-made from colourmen and art stores.[2] When water-based acrylics were introduced in the 20th century (in the early 1960s several companies introduced emulsion paints) they still, however, came with significant manufacturing challenges.

To overcome the challenges of grinding dry pigment directly into acrylic paint colourant dispersions (or pastes/slurries) became common in the 1970s.[3] These are highly concentrated, water-based precursors that allow a thorough grinding of the pigment without having to contend with the many other ingredients of acrylic paint. Many of us will be familiar with a similar product and concept, the liquid colourants added to an uncoloured can of commercial wall paint at a hardware store. These products however cannot hold a candle to artists quality paints that have been devotedly crafted.

Tri-Colour, Tri-Phase: Making Modern Pigment Dispersions

To produce colourful dispersions for acrylic paints, pigments are ground in three phases: wetting, dispersing and stabilizing. [4]  Most pigments are hydrophobic, meaning they do not mix with water, and would rather stick to themselves. Oil paints are at an advantage here, with many pigments readily absorbing oil and wetting out. Water-based dispersions thus require synthetic wetting agents. Although these may sound unfamiliar, wetting agents are nothing more than surfactants – the chemicals like sodium lauryl sulfate that make up our everyday detergents and soaps. They are molecules with polar and non-polar portions that bridge non-polar substances, like pigments, with highly polar water.

pigment float on top of water, and pigment dispersing into water.

Figure 3: Quinacridone red, without and with a dispersion agent (surfactant).

Tri-Art uses not one, but an array of surfactants that have come from years of testing. By carefully attuning the surfactant used, the maximum amount of pigment can be wet out and dispersed into the solution. By aiming for the highest concentration of pigment possible in these dispersions, Tri-Art has been able to create an incredibly high pigment load in their finest quality acrylic paints.

Once the pigment is wetted into water it is then ready for dispersion – the breaking of the aggregate particles. During this phase high mechanical forces are critical to grind the pigment. [5] At Tri-Art two processes are used to disperse the pigment as effectively and efficiently as possible. The first process is high speed mixing with a cowles blade. The outer edge of the blade reaches a speed magnitudes higher than the shaft of the mixer, thereby imparting high shear forces throughout the solution that break apart aggregate particles. This is typically able to produces particles smaller than 250 um, and comfortably within the range of 30-40 um that most artists pigments are formulated for use at.[6] For synthetic organic pigments like Quinacridone red that tend to stick together, a second step is necessary to further break up the very fine particles. Bead milling is able to decrease the particle size to less than ten um if desired. [7] This technique employees a cylinder filled with several kilograms of small industrial ceramic beads (less than two millimeters in diameter). The beads are spun by an agitator that cause the beads to collide with each other. Their resulting impact force grinds apart pigment aggregates between the ceramic balls. The process is energetic enough to produce a considerable amount of heat, so a constant flow of water in employed in a cold-water jacket to keep the dispersion from overheating.

pigment grinding article images 2021

Figure 4: No mullers will be found in modern paint making, instead a cowles blade and industrial ceramic beads (with pen for scale) are employed. Each bead is less than two mm in diameter.

pigment is mixed with an electric whisk into water. The mixture becomes a dark, saturated red, with a great deal of foam ontop.

Figure 5: Demonstrating dispersion by shear forces. A cowles blade is mimicked with a milk frother. This also emphasizes the need for another key additive in pigment dispersions: defoamers.

The last step of grinding the pigment into a concentrated solution is to stabilize the newly dispersed particles. Because of their affinity for each other, the particles must often be stabilized to prevent them from reforming the aggregate particles they once made up. Stabilizers are added that absorb onto the surface of each pigment particle, coating them in a repellent that balances all the particles an atomic distance apart from each other. These are most commonly acrylic polymer salts – chemically very similar to the acrylic polymers that will make up the finished paint, they will provide stabilization without interfering with the final formulation. The mixture can be further stabilized with acrylic resins (acrylic paint binder) forming a slurry that is then ready to be mixed into a multitude of paint formulations. [8]

Discerning Dispersions: Why Does the Quality of the Grind Matter?

Pigment grinding is critical to the final outcome of the paint because a high-quality grind allows for high pigment loading, but just as importantly, a high-quality grind allows for control of the pigment’s characteristic hue, transparency/opacity, gloss/matte qualities, and staining power. When it comes to single pigment artists’ qualities paints, it takes care to achieve not only an excellent quality pigment dispersion each batch, but one that is consistent from batch to batch too. For these single pigment paints, as the name suggests, any discrepancy in hue cannot be adjusted for with other colours – this would affect the mass- and undertones and colour mixing properties of the paint, critical for the painter who has selected these colours to work with.

Take for instance earth pigments like raw umber. It’s come be known as notoriously difficult pigment here at Tri-Art. The earth pigment contains a portion of inorganic iron oxide and another of organic carbon black. Inorganic pigments can typically be dispersed at high speed with a cowles blade in little time (20-40 minutes), but the organic carbon black remains as undispersed particles. The resulting colour is warmer than should be, with considerable streaks. Some manufactures might simply stop here with a ‘time is money’ attitude, but at Tri-Art we persevere on until all portions of the pigment are full dispersed – a product of careful surfactant attenuation and further grinding processes.

A draw down card of two raw umber samples and a macro detail shot of raw umber paint with pigment particles visible.

Figure 6: Far Left, draw down of raw umbers. Left, standard well dispersed dispersion. Right, carbon black has not been dispersed. Far Right, black particles of undispersed carbon black in raw umber paint.

In the lab we carefully test for the consistency of these colours with several methods: measuring the size of the particles with a fineness of grind gauge, making a small bespoke batch of paint to compare to our standards, and undertaking rub-up tests. The latter is particularly good for quick testing dispersions. A dispersion is coated onto a card and a small spot is rubbed (swirled) while still wet. After allowing it to dry, poorly dispersed, unstable particles will be shown by a colour change where the rub-up has disturbed them. In properly dispersed and stabilized mixtures the colour will remain largely the same, as the rub-up simply moves the homogenized, stable dispersion around. [9]

two paint draw downs with rub-up tests at their centre.

Figure 7: Left, a successful rub-up test. Right, an unsuccessful rub up test showing the disruption of poorly dispersed pigment particles.

Testing Handmade Dispersions

My own experiments with pigment grinding focused on two difficult pigments we work with at Tri-Art manufacturing: raw umber and quinacridone magenta. Quinacridone red is modern, synthetic, dye-like pigment. Its small organic particles would rather stick to each other than disperse into paint. I could tell just by looking at these pigment powders under magnification that I had some significant clumps that I would have to work out in this paint.

two containers of pigment, one red, one brown.

Figure 8: Quinacridone red pigment, raw umber pigment.

Watercolours are particularly suited to hand mulling. The (re)solubility of gum Arabic means that water can simply be dropped back onto the plate as the paint is being dispersed by the action of the muller. Here you can see that even with an initial mulling my raw umber paint has a gritty texture to it. Both paints at this stage were also lacking saturation, seen in my paint outs in the next figure. With successive mulling, the paints became smooth and pleasantly thick watercolour. I painted out more swatches as I went, watching the colour saturation increase as the pigment particles were dispersed.

Samples of watercolour during mulling with a glass muller.

Figure 9: Left, Mulled watercolour medium and raw umber. Right, After successive mulling, smooth, quinacridone red watercolour.

Paint outs of watercolours, both brown and red. Three samples each show the watercolour becoming more saturated and even in colour.

Figure 11: Good, better, best. Watercolour dispersions.

Despite several minutes of mulling the paint mixture, some particles are still apparent in the paint out of raw umber, but overall, I was very happy with results. Hand mulling pigment and watercolour medium resulted in a richly pigmented paint that showcased the vivid and chromatic quinacridone red and brought out the coolness of the raw umber. With a successful start, I turned my attention to the real challenged, could I mix a workable paint with pigment and acrylic medium?

Final images of watercolours made by hand dispersion with glass muller. Two pans of red and brown and two paint outs.

Figure 12: Final paint outs of handmade watercolour. Raw umber still shows undispersed particles.

Mixing raw umber pigment directly with acrylic medium with just a palette knife produced a gritty paint that very quickly highlighted for me the difficulties of grinding pigment directly into acrylics. The medium dried so quickly that little time was available for me to work the pigment into the paint. Adding more medium allowed me a longer working time, and with this I achieved a slightly less gritty texture, but not one that I would deem successful by any means. I knew that if the inorganic particles of iron oxide I could see were not being dispersed, the much smaller carbon black for sure were still largely clumped together as well.

a palette knife, acrylic medium, and dry umber pigment in the first image is mixed into a slightly gritty paint in the second.

Figure 13: Hand dispersing dry raw umber into acrylic medium. Right, First attempt at directly grinding dry pigment into acrylic medium.

An image of brown acrylic paint after further hand mixing and medium added, the paint has smoothed out.

Figure 14: Results of further mixing and addition acrylic medium added (dry pigment directly into acrylic medium).

Despite being a much finer particle, quinacridone red didn’t fare much better. I needed a liquid dispersion that I could grind then incorporate into the fast-drying acrylic. With my fresh, successful watercolour at hand I attempted a slightly unconventional pairing. A mixture of watercolour and acrylic produced a richly pigment paint film, one that seemed promising at first. After allowing my paint to dry, I notice both films had a considerable concentration of aggregated particles – perhaps pigment, perhaps slightly dried medium from the mixing process. The glossy richness faded, leaving a dull matte surface that no longer showcased the vibrancy of my quinacridone red. While certainly not a combination I would ever advise for a working artist, the experiment solidified for me the difficulties of working pigments and water-based acrylic mediums.

A sample of red paint, photographed in normal and raking light to showcase both the saturation of colour, but also the particles still apparent.

Figure 15: Quinacridone red handmade acrylic paint. The right image in raking light shows the aggregated particles that formed in the paint.

Back to the Grind: The Everyday Takeaways of Pigment Grinding

It may require the careful finesse of an expert paint maker, but the benefits of properly ground pigments are clear. An excellent dispersion allows for the formulation of paint that is smooth (it never should be gritty) while balanced with a range of high to low gloss specific to each pigment. Furthermore, it creates paint with a consistent mass- and undertone that allows for tinting and colour mixing without a tendency towards a lack of chroma or muddy hues. If you find that a drop of titanium white turns you colours ‘beyond the pale,’ that your colours lack saturation, your glazes are hazy, or your paints have little covering power, you may want to consider evaluating the quality of your paints – especially when it comes to acrylics.

When selecting acrylic paint, be sure to choose only artists quality acrylics, made by a reputable brand that stand by their products. If budget is a consideration for your work, be sure to do your homework before purchasing what is simply within your reach. Pigments, by a lion’s share, are the most expensive part of any paint formulation. Manufacturers that take the time to fully grind and disperse pigments can utilize less pigment to produce their budget lines, while retaining quality of colour, without the use of cheap fillers. Not only can expert pigment grinding amount to savings on the upfront cost of a budget quality line, but also the cost-per-use, as these are generally higher quality products with more saturation and staining power. By mastering pigment grinding for our own finest quality artists lines at Tri-Art, we are also able to offer a high quality student and kids line, at a very competitive price as well.

blue high viscosity paint on a paint brush

[1] Wetting and Dispersing Additives (BYK Additives and Instruments).

[2] George O’Hanlon, ‘Traditional Oil Painting: The Revival of Historical Artists’ Materials – Natural Pigments’, Natural Pigments, 2013 <> [accessed 19 January 2021].

[3] Antti Mäntynen and others, ‘Optimization of Grinding Parameters in the Production of Colorant Paste’, Powder Technology, 217 (2012), 216–22 <>.

[4] Wetting and Dispersing Additives.

[5] Christiana Agbo and others, ‘A Review on the Mechanism of Pigment Dispersion’, Journal of Dispersion Science and Technology, 39.6 (2018), 874–89 <>.

[6] Mäntynen and others.

[7] Mäntynen and others.

[8] Wetting and Dispersing Additives.

[9] Wetting and Dispersing Additives.


Agbo, Christiana, Wizi Jakpa, Bismark Sarkodie, Andrews Boakye, and Shaohai Fu, ‘A Review on the Mechanism of Pigment Dispersion’, Journal of Dispersion Science and Technology, 39.6 (2018), 874–89 <>

Mäntynen, Antti, Alexey Zakharov, Sirkka-Liisa Jämsä-Jounela, and Mats Graeffe, ‘Optimization of Grinding Parameters in the Production of Colorant Paste’, Powder Technology, 217 (2012), 216–22 <>

O’Hanlon, George, ‘Traditional Oil Painting: The Revival of Historical Artists’ Materials – Natural Pigments’, Natural Pigments, 2013 <> [accessed 19 January 2021]

Wetting and Dispersing Additives (BYK Additives and Instruments)


Modern and Post-Modern Pigments: Cadmiums vs. Bismuth Yellow and Pyrrole Red

Painters today are offered a considerable breadth of choices when selecting paints. It’s easy to become overwhelmed. We might default to using the pigments our instructors taught us to use or those we have simply used for many years. The wide accessibility and relative affordability of so many pigments is nothing short of modern miracle, sustained on by a global system of trade and manufacture. Rather than fear the long shelves of unfamiliar pigments I hope I can convince you that these options are often solutions to our artistic aims.

Those new to painting may search ‘essential paint colours’ and find most lists include some variation of cadmium yellow and red. These are the iconic, bright, opaque colours that have been loaded onto painters’ palettes for nearly two centuries now. Today’s article makes the case for cadmium’s post-modern ancestors, bismuth yellow and pyrrole red. Where did these pigments come from and why should you choose them instead of cadmium colours?

drawdown swatch of yellow and red

Figure 1: Cadmium Yellow (Medium, PY 35), Bismuth Yellow (Medium, PY 184), Cadmium Red (Medium PR 108), Pyrrole Red (opaque, PR 254)

Heavy Hitters: A history of Cadmium Pigments

Although they may seem firmly historical, heavy metal cadmium pigments (red, yellow and orange) actually have somewhat recent history, but certainly one that has made a prolific splash. The critical elements of these iconic colours, cadmium and selenium, were not discovered until 1817.[1] When the German metallurgist Friedrich Stromeyer discovered cadmium in 1817, he immediately recommended his brightly coloured cadmium sulphide compound for use as an artist’s pigment. It would take the work of another chemist, the Swedish Jöns Jacob Berzelius, with his discovery of selenium, to make orange and red shades of cadmium with the addition cadmium selenide to Stromeyer’s cadmium yellow.[2] Cadmium pigments now also contain a portion of zinc sulphide which in combination with yellow cadmium sulphide which yields cool, light hues of colour like cadmium yellow primrose.[3]

a row of cadmium paint swatches from yellow to red

Figure 2: Tri-Art High Viscosity Clinically Pure Cadmium Colours: Yellow Light (PY 35, with the most zinc sulphide), Yellow Medium (PY 35), Orange (PO 20, with increasing cadmium selenide), Red Medium (PR 108, with the most cadmium selenide).

Cadmium pigments appears as early as 1829 in oil paintings in France and Germany but were slow to take off. Cadmium pigments were not commercially available until 1840[4] with a very limited supply of raw materials – to this day there are no readily accessible sources of cadmium and selenium, and so these components must be processed out of other mining waste. [5] Scarcity persisted throughout the 19th century with one first-hand account from 1888 noting cadmium yellow as “a perfect colour if not so expensive.” [6]

Despite their cost, these pigments gained popularity for their enduring colour, especially in the heavily polluted air of 19th century coal-burning cities.[7] They found use in oils and watercolours, where small amounts of the costly pigments could be appreciated. The famous colours of the Impressionists certainly owe a great dept to the bright, opaque shades of cadmium colours that added chroma to their a la prima palettes. Monet’s works have been extensively documented to contain cadmium yellow, as seen in the warm yellow hues of Bordighera (1884).[8]

a painting, bordighera by claude monet

Figure 3: Claude Monet, Bordighera, 1884, The Art Institute of Chicago, Illinois. Public Domain, circa wiki Images.

The 1920s brought the industrialization of cadmium pigments. It was discovered that cadmium colours could be extended with inexpensive lithopone filler while still remaining colourful and opaque. With this, cadmiums became one of these most important commercial pigments, still being produced in mass quantities to this day. [9] Quality artists’ paints continued to use unadulterated cadmium colours to capitalize on the vibrancy of these pigments, but at a premium cost. The ubiquitous nature of these colours on nearly any painter’s palette is a testament to their beloved working qualities, and perhaps lack of alternatives.

Bismuth as Usual? The Long History of A Post-modern Yellow

You may be familiar with bismuth metal in its crystallized state, an impossibly geometric and prismatic structure, commonly sold in shops. While these are modern synthetic crystals, bismuth as a white metal was known to the ancients and found use in artworks as early as the 15th century. The metallic quality of bismuth meant it could be utilized as an economical substitute for silver, most commonly found as a powdered pigment for illuminating of manuscripts or oil paintings.[10] The pigment was likely more grey than metallic, with a slight lustre similar to metal-point drawings or modern graphite. Painters like Francesco Granacci (1469–1543) may have tried to utilize this lustrous quality when painting metallic surfaces like the armour in Portrait of a Man in Armour (ca. 1510). Modern analysis found the grey to be bismuth based.[11]

synthetic bismuth crystal

a painting, a portrait of a man in armor

Figure 4: Modern Synthetic Bismuth Crystal by Dschwen. CC 2.5. Via Wiki Images.
Bismuth Metal Ingots. By Unconventional2 – Own work, CC BY-SA 4.0, via Wiki Images.
Francesco Granacci (1469–1543), Portrait of a Man in Armour (ca. 1510). National Gallery of Art, Washington DC. Public Domain, via Wiki Images.

Metallic bismuth as a pigment does not appear to have gained wide traction in history, and only in the 20th century was the metal explored for its colorful possibilities. Beginning in the 1960s the spectral effect of bismuth crystals was capitalized on in the form of a nail polish additive – bismuth oxychloride was utilized as a replacement for naturally pearlescent materials.[12] Contemporary bismuth yellow pigments were only introduced to market in 1985 after many decades of experimentation.[13]

3 bismuth yellow colour swatches

Figure 5: Post-modern yellows. Tri-Art Liquids Bismuth Yellow (PY 184) in Light, Medium and Deep Hues.

Bismuth Yellow (labeled PY184 on artists paints) is a mixture of two metal oxides, bismuth vanadate and bismuth molybdate. Bismuth vanadate was first synthetized in 1924 for pharmaceutical purposes. In 1976 DuPont began developing this compound as a pigment. They described their bismuth vanadate as ‘brilliant primrose yellow.’ Mixed metal oxide version of vanadate and molybdenum were later synthesized, giving rise to warmer orange-red shades.[14] Tri-Art offers shades from light to deep, similar to shades of cadmium yellow. Approximately 900 tonnes of bismuth yellow are now produced annually, [15] largely for industrial, outdoor applications due to its outstanding lightfastness.

Pyrrole Reds: A Fiery Future

Pyrrole red is a relatively new pigment – it was first synthesized in 1974 by accident. [16] Despite its infancy, many of us will have encountered this pigment in everyday life, the pigment has become widely used in automobile paints, plastics and cosmetic formulations (labeled CI 56110).[17], [18]

two pyrrole red swatches

Figure 6: Tri-Art Liquid Acrylic Pyrrole Red Light (PR 255) and Medium (PR 254).

When pyrrole red was first synthesised, the accidental biproducts had enticing properties as pigments: highly insoluble, highly stable, and intensely red in colour. The product had an incredibly high chroma red colour due to their synthetic, high purity.[19] The pigment was first introduced as Irgazin DPP in the 1980s by Ciba-Geigy.[20] It now comes in a range of hues from orange to bluish-red.[21] Tri-Art offers pyrrole red light and medium in similar shades to cadmium reds.

Modern vs. Post-Modern pigments: Which are better?

Cadmium pigments are considered staple of the serious painter’s palette – intensely opaque, they offer great colour coverage and tinting strength, especially when mixing with titanium white. However, cadmium colours have always been cost prohibitive and will continue to be so due to the scarcity of available cadmium and selenium on earth. Cadmium pigments also have record of causing problems for painters and conservators. In their 19th century infancy cadmium pigments were particularly unreliable; contaminants left over from the processing of cadmium pigments from raw ore could cause disastrous deteriorations to painted surfaces in just a few decades. Many 19th century paintings with once bright, richly saturated yellows now appear bleached white, cloudy, or chalky in appearance. Several cases show the opposite effect too, with mixtures of cadmium yellow and other pigments like chrome yellow and the famous Emerald Green (composed of deathly toxic arsenic) inciting reactions that markedly darken the paint film. It really took the improvements of 20th century chemistry to bring us chemically pure cadmium pigments that were consistently stable in the 1940s.[22]

Despite finding stability in chemically pure formulations, cadmium pigments remain problematic because of their heavy metal nature. Toxicological and environmental impacts are something that every painter should consider when deciding if they want to use these pigments. Because of these issues, pyrrole red and bismuth yellow are often suggested as replacements for these pigments. Pyrrole red is nearly just as opaque as cadmium red, intensely red, outstandingly light-fast, and non-toxic. [23] Because of its safety profile, the pigment is safe enough to be used in tattooing, cosmetics and all paint formulations. Unlike cadmium colours, post-modern pigments like pyrrole red and bismuth yellow can found in liquid and spray paints – cadmium colours, in contrast, should not be sprayed to avoid any inhalation.

cadmium red swatches next to pyrrole red swatches

Figure 7: Tri-Art High Viscosity Acrylics. Cadmium Red (Medium Shade, PR 108) and Pyrrole Red (medium shade, PR 254). Straight from the tube, as a tint with titanium white (PW 6), and as a wash with water.

Bismuth yellow is similarly non-toxic, with a very high opacity, and an intense yellow colour. Although a metal oxide, it appears that bismuth yellow is an environmentally conscious choice with impact studies noting virtually no risk to human or aquatic life.[24] Bismuth yellow also has excellent lightfastness, being used extensively for outdoor applications.[25] Like cadmium pigments, bismuth yellow is an expensive pigment, owing to the cost of raw materials. Like cadmium, bismuth is somewhat scarce and therefore can only be sourced as a biproduct of mining other metals.[26]

cadmium yellow swatches next to bismuth yellow swatches

Figure 5: Post-modern yellows. Tri-Art Liquids Bismuth Yellow (PY 184) in Light, Medium and Deep Hues.

Pyrrole red has the additional advantage of coming in a range of not only shades, but also transparency. Unlike cadmium colours, the particle size of pyrrole red can be manipulated to make transparent and opaque formulations. Painters may be more familiar with this colour than they think – transparent pyrrole red has been used to create the red filter of RGB type LCD screens.[27] Although these screens project colour rather than reflecting it as in a painting, modern artists may find they can reproduce the high chroma colours we see every day through our screens more faithfully using contemporary pyrrole pigments versus muddier cadmium colours. Transparent pyrrole reds are additionally more lightfast than many other transparent reds that are used to formulate colours like alizarin crimson.

red drawdown colour swatch

Figure 9: Tri-Art Liquid Acrylics, Transparent and Opaque Pyrrole Red, Medium Shade (both PR 254).

a macro example rgb pixels displaying different colours

Figure 10: LCD screen showing individual pixels of red, green and blue. The red filter can be made using transparent pyrrole red. By Luís Flávio Loureiro dos Santos, via Wiki Images. CC 3.0.

Testing out Bismuth Yellow, Pyrrole Red and Cadmium Colours

Advantages of Pyrrole Reds:

  • Pyrrole red is non-toxic, and more ecologically friendly than cadmium colours.
  • Despite its price point, the very high tinting strength of Pyrrole red allows this colour to go very far – Tri-Art’s high quality, highly pigmented, professional formulations further ensure you get the most pigment and colour possible.
  • Pyrrole colours are the closest alternative to cadmium colours rather than cadmium hues currently on the market.[28] Hue colours must balance an accessible cost with replicating the hue of another pure pigment. If you are looking to replace heavy metal pigments like cadmiums from your palette at a professional level – pyrrole is the best choice.
  • Pyrrole red creates cleaner secondary colours, less warm and muddy than cadmiums. Its high chroma also competes better with other high chroma colours like phthalo blue and high tinting colours like titanium white.
  • Pyrrole red has options for opaque and transparent variations – if you can become familiar with its colour properties you can readily extend your working palette to transparent reds rather than reaching for other hues of red.

cobalt and magenta paint swatches

Figure 11: Cobalt Blue and Manganese Blue Hue (phthalo blue) mixed with cadmium red (left row), pyrrole red (right row), and the resulting mixtures with titanium white (bottom row). Pyrrole red created a richer purple with both blues, while cadmium produced warmer, muted hues. When up against titanium white, pyrrole red colours remained more saturated in chroma, with cadmium colours becoming even more muted.

bismuth, cadmium, and pyrrole swatches on two cards

Figure 12: Bismuth Yellow (left) and Cadmium Yellow (right) mixed with cadmium red (left row), pyrrole red (right row), and the resulting mixtures with titanium white (bottom row). Results were similar to mixing purple secondaries, with pyrrole red producing richer, more saturated colours, even when mixed with titanium white.

Advantages of Bismuth Yellows:

  • Bismuth yellow is ecologically more friendly than cadmium colours and non-toxic.
  • Like pyrrole red, bismuth yellow creates cleaner secondary colours. I found bismuth yellow most convincing when mixing green hues – it readily produced more neutral greens than cadmium yellow that always appeared yellow and warm shaded.
  • Last year Tri-Art introduced a newly modified bismuth pigment which improved grinding and dispersing for their bismuth yellow acrylic paint. The new pigment creates a paint with higher gloss, greater chroma and saturation, and requires a less energy intensive process to create.

cobalt and manganese swatches

Figure 13: Cobalt Blue (left) and Manganese Blue Hue (phthalo blue)(right) mixed with cadmium yellow medium (left row), bismuth yellow medium (right row), and the resulting mixtures with titanium white (bottom row). Bismuth yellow created a more neutral green when mixed with both blues, while cadmium produced warmer, yellow hues.

By now all but the traditionalist painter might be convinced of these contemporary pigments. But for those who would like to replicate the works of 19th and 20th century geniuses I would offer one last thought. While making my colour charts, I also found that bismuth yellow was able to make a beautiful shade of bright and cool green with phthalo blue and titanium white – the colour reminded me of the infamous Emerald Green. Thankfully no longer available due to its incredibly toxic arsenic content, the bright and densely opaque green colour dominated the art world of the 19th century. Degas possibly used the pigment when painting his ­Dancer with Bouquets (1895-1900), adding bright flourishes of cool green. Whatever your artistic aims, I would suggest that pigments like pyrrole red and bismuth yellow offer painters, both modern and classical alike, the ability to mix a wider range of colours while retaining vibrancy and saturation when creating tints with titanium white. Consider trying them for your next project.

painting of ballerina on stage with bouquets at her feet, showing use of emerald green

Below, Bismuth Yellow, phthalo blue and titanium white mixtures

Figure 14: Edgar Degas, Dancer with Bouquets, 1895-1900, oil on canvas. Chrysler Museum of Art. Public domain. Below, Bismuth Yellow, phthalo blue and titanium white mixtures. The bright touches of green in this work are possibly the infamous arsenic based emerald green, a colour that can no longer be obtained. Replicating the colour with modern pigments like bismuth yellow worked better than cadmium colours.

When to reach for Cadmium Reds and Yellows:

Despite their drawbacks, cadmium colours will continue to hold an important place in the painters’ palette. For the contemporary painters looking to evaluate their painting practice you may want to consider using cadmium colours for the follow purposes:

  • Trying to replicate a historical palette (note that many historical colours are not available due to their toxicity or fugitive nature)
  • Opacity is critical (pyrrole red and bismuth yellow are slightly less opaque than cadmium colours)
  • You are looking to achieve a palette that is warm or low in chroma while keeping colour mixtures minimal
  • For those on a budget, cadmium hue colours can be explored too. However, these will be most useful for those who paint straight from the tube, without extensive colour mixing.


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