With Rhodanine copper staining, which counterstain is used?

• A. Mayer’s Hematoxylin
• B. Eosin
• C. Papanicolaou
• D. Safranin

Answer: (A)

Rhodanine copper staining highlights copper deposits in a red-orange color, so a blue nuclear counterstain is used to provide clear contrast and preserve tissue detail. Mayer’s hematoxylin is the common choice because it stains nuclei blue-black without overpowering the copper signal, making the copper deposits easy to identify against the labeled nuclei. Using eosin would add pink/red cytoplasmic staining that can blur the red-orange copper stain, and Papanicolaou or Safranin aren’t standard counterstains for this histochemical protocol, as they don’t provide the same crisp nuclear contrast needed to visualize the copper deposits effectively.