Now discontinued, previously a star of 20th century palettes, and still fades: Alizarin Crimson (Genuine). The "genuine" part must now be added since the pigment is now discontinued and imitations already abound. The natural form of Alizarin Crimson is NR8, and the pigment discussed here is its synthetic version, PR83. This is a rich gem-like crimson that is has been incredibly difficult to replace. It is baffling that it is so difficult to imitate exactly. Alongside its beauty, painters have been plagued with a quandary: what does one do about its terrible lightfastness? PR83 is often used as a fading pigment by which to judge the lightfastness of other colors- unfortunately Alizarin tends to loose its lightfastness that reliably. In addition to the fading this pigment has issues with cracking, which is less often discussed, but nonetheless reported to be an issue. It requires a lot of oil to turn it into an oil paint.
Another issue which many never thought to consider is that chemically, both artificial and natural alizarins are actually incredibly similar to cancer-causing anthraquinones. It may also cause allergies. Monona Rossol's work on pigments contains more information.
Alizarin Crimson was beloved in the 20th century as the choice for a blue-leaning red, and many painting books recommended it despite its poor lightfastness. The lightfastness issue seems to be even worse in watercolor than in oil. So, due to its poor performance, genuine Alizarin Crimson cannot be recommended, but in any case it is now in the process of actually disappearing by way of discontinuation.
In 2023 or 2024 it was phased out by pigment makers, however some paint companies still have supplies of this traditional mainstay. It is incredibly difficult to replicate this pigment, and part of its mystery is a brown note hidden in the crimson. Alizarin Crimson a deep dark red, which is an area of the palette where painters can always use more pigments. Many companies have turned to PR177 as a permanent Alizarin. However, Virgil Elliott's tests revealed that in time PR177 also fades, despite the name "Permanent."
Some recommend PR264 Pyrrole Rubine as a replacement. Old Holland also has an interesting imitation blend to approximate genuine Alizarin.
Part of the complexity of genuine Alizarin is that it has two natures, the Alizarin and Purpurin. Oddly, the purpurin refers to an orangy note that fades out of natural madder preparations rather quickly. We have read that many versions of synthetic madder PR83 have had the purpurin (orange component) removed already, however some PR83s could theoretically have this. After the purpurin fades out the bluer red crimson will fade out as we are accustomed to seeing in lightfastness testing. In oils, this fading happens rather rapidly. Golden did some advanced lightfastness testing which studied concentration-dependent fading for Alizarin Crimson in particular.
