I finally decided to replace my Alizarin Crimson, which is only moderately lightfast (not that I ever really use it by itself in thin layers). I love the Alizarin by Williamsburg (dihydroxyanthraquinone, PR 83) and wanted to give their substitute a chance as I now go with them for all but one of my palette colors, so I tried their Permanent Crimson (anthraquinone, PR 177), which is described as an "absolutely permanent, lightfast substitute for Alizarin Crimson." Very disappointingly, Gamblin's Alizarin Permanent is made from a mixture of quinacridone red b (PV 19), perylene red (PR 149), and ultramarine (PB 29), so I'm not bothering with that. I read recently in at least three places that a truer substitute for the traditional Alizarin or madder hue is pyrrole ruby pigment (PR 264), which can be found in Rembrandt's Permanent Madder Deep (among others), so I got a tube to check it out.
Here I mixed a tint of each one with titanium white. I was afraid a photo would flatten any hue difference between the pigments, but except for the Permanent Crimson which seemed the tiniest bit warmer (this would create slightly less purple purples if you know what I mean), there was little hue difference for the camera to flatten. And all three pigments are strong-staining and have that lovely pinkish undertone. In masstone, however, the substitutes clearly don't match the Alizarin, in center, which is beautifully deep and dark as a thick pile (it almost resembles here a bleeding scab). The substitute Williamsburg, at left, feels flat, with little difference between its masstone and undertone. The Rembrandt pigment, while not an exact match, shows at least some of that Alizarin-like deepening as it gets thicker. Such deepness might not factor much in my normal painting work but it was something I was happy to see, so for this along with its excellent berry-juice-like quality overall, I'm going to try using the Permanent Madder Deep as my Alizarin substitute.