Theories of staining
* Physical theories :
1) Simple solubility e.g. Fat stains are effective because the stain is more soluble in fat than in 70% alcohol.
2) Absorption : This is a property by which a large body attracts to itself minute particles from a surrounding medium.
* Chemical theories :
It is generally true that acid stain basic element (cytoplasm) and basic dye stain acidophilic material (nucleus) however, this far from being complete truth, Indeed hematoxylin, which is an acid dye, does not stain the cytoplasm, but (in the presence of mordant) is one of the most widely used nuclear stains.