Tonight I am going to write about alizarin, well sort of. I don't use alizarin anymore and neither should you. I will come back to that.
Alizarin is one of several pigments that were derived since antiquity from the madder root. Madder was the source of the red that colored the coats of the British "new model army" that is, the famous redcoats. The ancient Egyptians used madder dyes.
In the 1860's German chemists developed a way to synthesize the red pigment in the lab. For over a hundred years alizarin served as the artists standard cool red pigment. However it was always problematic. Alizarin had permanency problems and had a bloody, blacky undertone. It was a more powerful pigment than the Rose Madder that was its natural counterpart. Rose madder, rare and expensive today was a common enough pigment fifty years ago ago. Rose madder was roseate in hue and had a lovely warm undertone that the alizarin didn't.
In 1958 Dupont developed quinacridone. It was a permanent, weather fast color that was used as an industrial coating and on cars. It was first used, to my knowledge, by artists, as permanent rose. Perhaps fifteen years ago artists began to convert to permanent alizarin, that is quinacridone. It is a great improvement, it has some of the roseate color of rose madder and the great pigmenting strength of alizarin. It comes in a range of colors through red to red-violet to violet.
So if you are still using the real alizarin (it will just say alizarin on the tube) you should switch to the permanent alizarin. It does cost as little more , but it isn't a color you will go through quickly. In return for that small investment you will get far better handling, clearer and more rose like color and permanence.
You might want to try permanent alizarin and permanent rose or quinacridone red (which is what I use) and decide for yourself which best suits you. As long as you are buying from a quality manufacturer and not buying a student grade it shouldn't matter too much which brand you buy.