2 different recipes. Brands sell different pigment mixtures under this name, so they won't all look or mix alike. Compare the pigments below; the most common is PR101 Red Iron Oxide.
Who makes it
PR101 Red Iron Oxide3
- Grumbacher Pre-Tested Artists' Oil No. P202
- Holbein Artists' Oil Color No. H347
Sizes are the ones each line is sold in; marks a size only some colors come in. Check the store for a particular color.