Which staining reagent is used to demonstrate elastic fibers as black in this staining sequence?

• A. Aldehyde fuchsin
• B. Ferric chloride
• C. Picric acid
• D. Methenamine silver

Answer: (A)

Visualizing elastic fibers requires a stain that specifically binds to elastin. Aldehyde fuchsin delivers a deep black color to elastic fibers because the aldehyde-containing dye reacts with the elastin, forming a stable complex that appears black against the background. This makes the elastic networks, such as those in vessel walls, stand out clearly in the staining sequence.

Ferric chloride is typically used as a differentiator in elastic fiber stains, not the color-determining reagent. Picric acid is commonly a counterstain or used in other stain formulations, not for producing black elastic fibers. Methenamine silver targets argyrophilic structures like basement membranes and reticulin and fungi, not elastic fibers stained black.