Which reagent is used for toning in Gomori's reticulin stain?

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Gold chloride is used for toning in Gomori's reticulin stain. After silver impregnation and reduction, toning with gold chloride deposits gold onto the existing metallic silver, which stabilizes the image and enhances contrast, helping the reticular fibers stand out against the background and making the stain more resistant to fading during processing. The other reagents play different roles: potassium permanganate may act as an oxidation step to modify background, ferric ammonium sulfate can act as a sensitizer to promote silver uptake, and formalin serves as the reducer to develop the silver image.