Acid Orcein-Iron and Acid Orcein-Copper Stains for Elastin

Paraffin sections of formol-fixed tissues stained 4-18 hr in 70% alcohol containing 1% orcein and 1% of concentrated (12 N) HCl by volume yield the familiar purple brown elastin and red nuclei on a pink background. When sections so stained are transferred directly from the stain to 70% alcohol containing 0.02% ferric chloride (FeCl₃·6 H₂O) or 0.02% copper sulfate (CuSO₄·5 H₂O) for a 15 sec to 3 min period, elastin coloration is changed to black or reddish black and chromatin staining to reddish black. The procedure can be counterstained with picro-methyl blue to yield blue collagen and reticulum or with our flavianic acid, ferric chloride, acid fuchsin mixture to give deep yellow background and deep red collagen.