What Is A Trichrome
The pedantic meaning of trichrome is three coloured. Apart from that there is no clear definition of what constitutes this kind of staining technique. A good basis for comparison is Masson's methods, but even this does not clarify the term since in some variants he used three dyes, and in others he used only two. Some people consider the nuclear stain as one of the colours, others do not.
Since counting colours is rather pointless, the term trichrome is used in this section of StainsFile to include any staining technique meeting the following criteria:–
These criteria include methods which demonstrate tissue components such as collagen and muscle, the most common purpose, but also includes methods for fibrin, pituitary cells, and those methods which include the staining of elastic with dyes such as orcein in a solution which also stains collagen and muscle. These latter methods are often called tetrachrome or polychrome methods, but for convenience are included with the trichrome methods.
Strictly speaking, the picro-fuchsin variants, such as the van Gieson and related methods, would be excluded by these criteria. It would also exclude methods which stain with a red acid dye, then apply a large molecular weight yellow dye in an anhydrous solvent. These are the Yellowsolve Methods. However, I include both of these groups due to their being dependant on the same fundamental processes as the true trichrome methods.