The bilirubin is the derived without iron of the biliverdin. In its turn, the biliverdin is the result of the degradation of the haemoglobin. 

The reaction happens mainly in the bony marrow, the spleen and the liver. 

In the liver of patients with obstructive icterus, the bilirubin appears as thrombi in the biliary canaliculus and granules in hepatocytes and cytoplasm of the cells of Kupfer The pigment is insoluble in water and in the aqueous fixative, but it can change to the green colour in case of extended formalin fixation. 

The colour developed from the reaction of Fouchet has had to one strongly oxidation - reduction of the complex and consequent transformation in biliverdin.

The Fouchet-Van Gieson stain is composed of 3 reagents for the visualization of bilirubin and collagen according to the Kutlick method.

Here are some examples of stains obtained with the coloring of Fouchet-Van Gieson

• Pigments of bile: blue / green
• Collagen: Red
• Muscle and cytoplasm: Yellow