The reducing agent in most reticulin stains is?

• A. Sodium thiosulfate
• B. Formaldehyde
• C. Uranyl nitrate
• D. Gold chloride

Answer: (B)

The main idea here is that the reticulin stain relies on a silver development step where silver ions are reduced to metallic silver so they deposit along the delicate reticular fibers. Formaldehyde is the reducing agent used in most reticulin protocols; during development it donates electrons that convert Ag+ ions into Ag0, producing the characteristic black reticular network against a lighter background. Sodium thiosulfate isn’t the reducer—it’s used after development to remove unreacted silver and stabilize the image. Uranyl nitrate is a heavy-metal stain for contrast in other contexts, not the reducer in this stain, and gold chloride is used for toning to enhance contrast and permanence, not to reduce silver.