The developer in the Warthin-Starry stain is which chemical?

• A. Hydroquinone
• B. Silver nitrate
• C. Potassium permanganate
• D. Formalin

Answer: (A)

In this silver-staining method, the developer is the chemical that reduces the impregnated silver ions to metallic silver so the organisms stand out. Hydroquinone serves as the reducing agent in the development step of the Warthin-Starry stain, producing the dark metallic silver deposits that highlight bacteria against a lighter background. The silver nitrate solution is what provides the silver to be deposited, but the actual reduction to metallic silver—what creates the visible stain—is driven by hydroquinone in this protocol. Other reagents like potassium permanganate or formalin may play roles in background bleaching or in other silver-stain variants, but they are not the development agent used here.