Contemporary Ivory Black, or Pigment Black 9, is an inorganic synthetic pigment made from charred bones. This is the least pure form of carbon black, containing a high percentage of calcium phosphate. Perhaps because of these impurities, it offers a softer, even slightly 'grey' black, a favorite with many artists.
Is Ivory black suitable for vegans? No, because it is made from the bones of animals. A better choice would be a Pure Carbon Black or Lamp Black. Occasionally manufacturers use these terms interchangeably, so it's worthwhile to check their website for the specific origin of the pigment.