Muscle in a trichrome stain should be colored red. A number of conditions may result in muscle being unstained or stained grey.
Situation: muscle unstained or grey in a trichrome stain
Causes for the situation:
(1) depleted stain solutions
(2) formalin-fixed tissue that was not pretreated prior to staining
(3) overstaining with iron hematoxylin
(4) inadequate removal of unbound iron hematoxylin
Corrective action:
(1) Replace older solutions.
(2) Pretreat tissue fixed in formalin with Bouin solution, picric acid, or mercuric chloride before staining.
(3) Limit staining in iron hematoxylin.
(4) Wash thoroughly in 70% alcohol after staining in iron hematoxylin.
