Precipitation of the dye during staining with best carmine is due to evaporation of the ammonia; to avoid this, the working solution should be?

• A. Filtered and used in a closed container
• B. Kept at high temperature
• C. Used in an open container
• D. Agitated vigorously during staining

Answer: (A)

The stain relies on ammonia to keep carmine in solution; ammonia is volatile, so if it evaporates the solution becomes less alkaline, and the dye tends to precipitate during staining. Keeping the working solution in a closed container minimizes ammonia loss and maintains the intended pH and dye solubility. Filtering the solution removes any undissolved material or particulates that could serve as nuclei for precipitation, ensuring a uniform, clear stain.