Which fixative requires washing in buffer after fixation to prevent pigment?

Study for the CAMLPR Histology Practice Test. Study with flashcards and multiple choice questions, each question has hints and explanations. Get ready for your exam!

Osmium tetroxide is a lipid fixative that forms osmiophilic, dark deposits in tissue. After fixation, washing in buffer helps remove unreacted osmium and stabilizes pH, which prevents the formation of osmium-related pigment that can obscure structures and interfere with later staining. The other fixatives have different pigment issues (for example, formalin pigment is addressed by buffering; picric acid can leave a picric acid pigment that’s washed out with water; potassium dichromate can leave chromate pigments), but they are not specifically mitigated by a post-fixation buffer wash in the same way.