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 + PBr6 Brown Iron Oxide1
- Williamsburg Handmade Oil Colors No. 6001680PBk9 PBr6LF I Semi-opaqueSeries 1Hue37 ml tube · 150 ml tube · 8 fl oz can* · 16 fl oz can*About Williamsburg
Sizes are the ones each line is sold in; marks a size only some colors come in. Check the store for a particular color.