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
PBk7 Carbon Black + PBr7 Natural Iron Oxide + PR83 Alizarin Crimson1
- Grumbacher Pre-Tested Artists' Oil No. P021
Sizes are the ones each line is sold in; marks a size only some colors come in. Check the store for a particular color.