2 different recipes. Brands sell different pigment mixtures under this name, so they won't all look or mix alike. Compare the pigments below.
Who makes it
PBk9 Ivory / Bone Black + PY42 Yellow Iron Oxide1
- Holbein Artists' Oil Color No. H369PY42 PBk9 PW6LF II Semi-opaqueSeries A20 ml tube · 40 ml tube · 50 ml tube* · 110 ml tube*About Holbein
PBk6 Lamp Black + PBr6 Brown Iron Oxide1
- PW4 PW6 PBk6 PBr6LF I OpaqueSeries 140 ml tube · 60 ml tube* · 225 ml tube · 1000 ml can*About Michael Harding
Sizes are the ones each line is sold in; marks a size only some colors come in. Check the store for a particular color.