Mayer’s carmalum staining mixture
1.0 g carminic acid (C.I. 75470; not to be confused with carmine)
10 g aluminum potassium sulfate (KAl[SO4]2•12H2O)
200 mL H2O
Combine above reagents and heat until boiling. Allow to cool to room temperature. Filter. Add as an antibacterial preservative:
1.0 mL formalin (37%-40% HCHO)
The solution loses most of its potency after 2-3 wk.
