Hello. New member chiming in.
Old Holland's Alizarin Crimson Lake Extra is a mixed color, I'd like to point out - Pr 19, Pr 177 & PBr 23. The purest Alizarin I have is from Harding. According to him it's from coal-tar not madder root (PR 83.). Now the color codes, as many folks know, can be misleading. W&N states their Alizarin Crimson 1 Artist Oil is PR 83, but the pigment is described as 2-dihydroxyanthraquinine lake. I've nothing against synthetic pigments (even have a W&N Permanent Alizarin,) but find they tend to not tint as well as natural pigments.
http://www.oldholland.com/pages/oil/x5.html
http://www.michaelharding.co.uk/colour-info.php?cID=98
http://www.winsornewton.com/leaflets/EN/AOCEnglish.pdf