The Accidental Invention of Pyrrole Red, a Modern Pigment

Pyrrole Red is a modern bright red pigment. Its name comes from the Greek word pyrrhós, which means ‘fiery’. Pyrrole Red was discovered accidentally in the 1970s and today it is a popular alternative to Cadmium Red, which was introduced at the turn of the 20th century. This article will explore how Pyrrole Red was invented, how it has been used in the car industry, and how it compares to Cadmium Red.

The Development of Pyrrole Red

In 1974, chemist Donald G. Farnum and his team at Michigan State University accidentally invented Pyrrole Red. At the time they didn’t think much about their creation and its potential, but they wrote about it in a British chemistry journal.

Later, a Swiss company called Ciba Specialty Chemicals found the report and in 1983 they patented a process for making the pigment based on Farnum’s findings. Speaking thirty years later, Farnum said he wished he had known how useful it could be when they first discovered it.

Jackson’s Artist Pigment Pyrrole Red (PR254)

Pyrrole and ‘Ferrari Red’

Because Ciba owned the patent, when the pigment came to market it was very expensive. However, car manufacturers were willing to pay the high price because it was ideal for car paint. Cars are outside for the majority of the time, so the pigments used to colour them need to be very durable. Pyrrole Red has excellent lightfastness, chemical stability, and weatherability.

Liquitex Heavy Body Acrylic Pyrrole Red (PR254)

One of the most famous uses of the pigment is by Italian car manufacturer Ferrari. Red has been the colour of Italian motor racing since the 1920s, and Ferrari has used many shades of red over the years. But Pyrrole became the colour most people think of when they think of Ferrari. In the early 1990s, 85% of Ferraris were painted red, and Pyrrole Red became known as “Ferrari Red.”

Pyrrole Red in Art

The same things that make a pigment ideal for car paint can also make it popular with artists. Because they are very bright, stable, and lightfast, Pyrrole pigments are now found in many professional paint ranges. It has also been used to spot fake paintings. In the 2000s, a series of paintings thought to be by Jackson Pollock were found to contain the pigment. Since Pollock died in 1956 and Pyrrole Red wasn’t invented until the 1970s, the authenticity of the paintings was thrown into question.

There are three Pyrrole pigments used in artist paints, which follow a pattern similar to the varieties of Cadmium Red pigment, which consist of light, medium, and deep shades:

PR254 – the classic ‘Ferrari Red’
PR255 – a brighter, more orange colour
PR264 – a deep burgundy

Pyrroles are often recommended as less toxic alternatives to Cadmium Red. The invention of Cadmium Red built upon the chemical innovations of the 19th century. Cadmium was identified as a metallic element in 1817, and Cadmium Yellow (cadmium sulphide) was introduced in the 1830s. The red-shade of the pigment was produced by roasting cadmium sulphide with selenium, and by the 1920s it was being used in the artist palette. Cadmium pigments are potentially harmful if inhaled and ingested, and in recent years there has been much debate over their continued use in artist paints.

In the following tests, I compare Pyrrole and Cadmium Red. Colour characteristics like hue, tinting strength, and saturation can vary between brands, but I have chosen paints that I believe are generally representative of the pigment.

Pyrrole Red vs. Cadmium Red

On a chemical level, the two pigment families are very different. Cadmium pigments are based on metallic compounds, making them inorganic, while Pyrrole is an organic pigment, meaning that it is based on carbon and hydrogen bonds. Nevertheless, when they are compared straight from the tube, they appear to be quite similar.

Top row, from left: Golden Heavy Body Acrylic Paint Pyrrole Red Light (PR255)
Michael Harding Oil Paint Pyrrole Red (PR254)
Isaro Watercolour Paint Pyrrole Red Deep (PR264)
Bottom row, from left: Jackson’s Professional Oil Paint Cadmium Red Light (PR108)
M.Graham Watercolour Paint Cadmium Red (PR108)
Jackson’s Professional Acrylic Paint Cadmium Red Deep (PR108)

The most obvious difference is that the Cadmium Red Medium is a little more muted than the middle shade of Pyrrole Red, but it’s important to allow for the fact that Cadmium watercolours tend to become a little duller when they dry. Pyrrole Red Deep is darker in value than the corresponding Cadmium Red Deep, but overall they are pretty close in hue.

When mixing the pigments with white, more differences are revealed. Both Pyrrole and Cadmium pigments follow the same pattern; the light shades (on the left) have peachy, orange undertones, and the deep shades have a more blue bias.

Top row, from left: Golden Heavy Body Acrylic Paint Pyrrole Red Light (PR255)
Michael Harding Oil Paint Pyrrole Red (PR254)
Isaro Watercolour Paint Pyrrole Red Deep (PR264)
Bottom row, from left: Jackson’s Professional Oil Paint Cadmium Red Light (PR108)
M.Graham Watercolour Paint Cadmium Red (PR108)
Jackson’s Professional Acrylic Paint Cadmium Red Deep (PR108)
Middle rows: Each colour tinted with Titanium White (PW6)

However, there is a noticeable difference in saturation. The Cadmiums produce quite muted tints, while the Pyrroles have retained their high chroma. The Pyrrole Red Deep in particular creates a rich, wine-purple when mixed with white, while the Cadmium Red Deep makes a more earthy, low-chroma tint.

Powerful opacity is a classic characteristic of a Cadmium pigment, whether it is red, orange, or yellow. It is one of the reasons that the Cadmiums have remained enduringly popular from their invention in the 19th century until the present day.

Opacity test with paint at full strength (top row), in 20% dilution (middle row), and 50% dilution (bottom row)
From left: Jackson’s Professional Oil Paint Cadmium Red Light (PR108)
M.Graham Watercolour Paint Cadmium Red (PR108)
Gamblin Artist Oil Paint Cadmium Red Deep (PR108)

The high covering power of Cadmium pigments is really extraordinary. Even when extended by 50% with a medium (the lowest black strip on the below test) they are barely semi-transparent. The Cadmium Red watercolour is less opaque than the oil and acrylic examples, but that is expected with a watercolour paint.

Pyrrole pigments can vary from transparent to opaque depending on how the pigment has been formulated, but looking at the coverage information of a wide range of Pyrrole paints, the vast majority are semi-transparent or semi-opaque. This is the case for the three Pyrrole pigments tested here.

Opacity test with paint at full strength (top row), in 20% dilution (middle row), and 50% dilution (bottom row)
From left: Golden Heavy Body Acrylic Paint Pyrrole Red Light (PR255)
Michael Harding Oil Paint Pyrrole Red (PR254)
Isaro Watercolour Paint Pyrrole Red Deep (PR264)

Even when used straight from the tube, they still allow the black gesso to show through. However, there are some Pyrrole paints that claim to be opaque, so I tested those separately to see how they compare with the Cadmium Reds.

Opacity test with paint at full strength (top row), in 20% dilution (middle row), and 50% dilution (bottom row)
From left: Liquitex Heavy Body Acrylic Paint Pyrrole Red (PR254)
Golden Heavy Body Acrylic Paint Pyrrole Red Dark (PR264)

Neither are opaque enough to measure up to the high coverage of a Cadmium paint. This is something to bear in mind if you love the opacity of Cadmiums and are looking for a less toxic alternative.

Pyrrole pigments do not have the toxicity concerns associated with Cadmium Red, but there are some characteristics that Pyrrole does not match. Cadmium Reds are always opaque, but most Pyrrole paints are semi-transparent or semi-opaque. They are also generally more vibrant and higher in tinting strength than Cadmium Red. Some artists will see this as an advantage, but others might miss the subtle earthiness that Cadmiums bring to mixtures.

It can be argued that it is more helpful to assess pigments on their own merits, rather than in comparison to another. Both Pyrrole and Cadmium Reds play slightly different roles in the artist palette, and can be used together or separately as unique pigments in their own right.

Further Reading

The Story of Vermilion Red

Colour Mixing: Eight Reds in Six Restricted Palettes

Recreating the Colour Palette of John Constable

Monotype Printmaking for Beginners

Shop Pyrrole Red on jacksonsart.com