The making of the Ivory Black was first described in the 4th century B.C. Ivory scraps were packed into clay pots and covered with an iron lid, leaving as little air as possible in the pots. The ivory was then exposed to high heat. This produced a very intense black, but was an extremely expensive process.
A cheaper method was invented by the Romans by burning ordinary animal bones instead of ivory. This became known as Bone Black and soon replaced Ivory Black in popularity. Artist started referring to Bone Black as Ivory Black and eventually the name stuck. So what we commonly know today as Ivory Black is actually...Bone Black.
True Ivory Black has a higher carbon content than Bone Black and is more intense. It is the deep velvety black found in the backgrounds of Rembrandt's portraits. The genuine pigment is still made in tiny quantities from Ivory harvested from animals that have died naturally but is almost as expensive as genuine Lapis Lazuli Ultramarine.
Ivory Black is a good, all purpose black that has a weak tinting strength and is slightly warm in color. This is a good choice for mixing greys, tinting and mixing with other colors.
A very slow drier in oil, it is not a good choice for an underpainting. It produces a soft and brittle oil paint. It can never be used in Fresco as it crystallizes.
Downsides: It is considered toxic. Do not breath dust. The slower drying time could be an advantage or a downside, depending on your preference.