Most silver stains use which of the following toning agents?

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

Answer: (D)

Toning in silver staining uses gold chloride. After the silver image is developed, applying gold chloride deposits gold onto the silver image, forming a gold-silver image that is more stable and resistant to fading. This toning step also produces the characteristic brownish-gold tone and helps sharpen contrast for clearer visualization.

The other substances serve different roles in the process. Sodium thiosulfate is used to remove unbound silver (a fixing step), not to tone the image. Formaldehyde acts as a reducing agent in the development step. Uranyl nitrate relates to uranium-based staining, not toning.