Earth colors must contain 70% or more combined iron evaluated as Fe₂O₃ by weight to classify under 282120. Natural ochres, siennas, or umbers below that threshold are generally classified elsewhere — typically among natural mineral substances — so laboratory analysis of iron content is essential for correct classification.

Surface treatment or micronization alone does not remove a product from heading 2821, provided the iron oxide remains the essential character of the article. However, if the pigment is formulated into a preparation with binders, solvents, or other additives that give it the character of a paint or coating, it would likely reclassify into a different chapter. A binding ruling is advisable for heavily formulated grades.