Stain uptake depends on the tissue element's affinity for the dye component of the stain solution. Affinity refers to the dye's tendency to transfer from a staining solution onto the tissue section. Table 1 lists factors that affect affinity and, ultimately, staining.
Table 1. Factors that Affect Dye Binding.| Factor | Description |
| Concentration of the dye | The higher the concentration of the dye, the more the dye is bound to tissue components.
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| Temperature | An increase in temperature increases the rate at which the dye diffuses throughout the tissue sample. It can also alter tissue components to be more receptive to dye penetration. |
| pH of staining solution | Cells and other tissue elements often have an affinity for stains/dyes with specific pH ranges. Therefore, the pH of the staining solution can directly impact the ability of a dye to bind with its intended tissue element.
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| Tissue fixation | Fixation alters and reorganizes specific molecular structures within the tissue sample such that there is increased permeability for staining. Unfixed tissue elements have limited binding sites for dyes. |
| Mordants | Mordants are chemicals that may be needed to bind dyes to certain tissue elements. They can also be used to intensify the staining results.
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