Final answer:
The cosmetic classification that requires sifting until free of coarse, gritty particles is powder, which ensures a fine texture and safe application for the skin.
Step-by-step explanation:
In the realm of cosmetics, the specific classification that requires sifting until free of coarse, gritty particles is powder. Powders are cosmetic products that must have a fine texture to ensure an even application and to prevent irritation of the skin. The process of sifting ensures that any large and potentially abrasive particles are removed, resulting in a smooth and comfortable product for the user.
Ointments, on the other hand, are generally semisolid preparations meant for topical application and do not necessarily undergo sifting as part of their processing. Similarly, emulsions, which are mixtures of two immiscible liquids like oil and water stabilized by an emulsifying agent, also do not require sifting to remove particles since their texture and uniformity are achieved through blending and stabilizing rather than removing coarse components. Thus, the correct answer to the student's question is that powders are the cosmetic classification that requires sifting until all coarse and gritty particles are eliminated.