Cosmetics Formulation Development

Hello, I would like to know which Black Iron Oxides should be used. It will be used with oil soap. I'm using activated carbon here, the soap is black, but when I put it in the compressor The soap came out, the color turned gray. The teacher taught me to use Black Iron Oxides but I see the company has 4 types (please suggest me which one should be used The color does not fade when compressing the soap. And the color is smooth, and it is used with oil soap (CP type).

Hello, use Iron Oxides Black (Ultra-fine, Silane-Coated) by blending with the oil in the recipe.