staining

Staining is the application of dyes or pigments to materials to highlight contrast, identify components, or impart color. It is used across disciplines to visualize structures in biological specimens, distinguish materials in research and diagnostics, color surfaces in materials and art conservation, and enhance the appearance of textiles and wood products.

In biology and medicine, staining increases visibility of cells and tissues under light microscopy. Dyes bind to specific cellular components, producing differential coloration that helps identify structures and abnormalities. Common techniques include simple staining and differential methods such as Gram staining for bacteria and acid-fast staining for certain pathogens, as well as special stains like silver or fluorescence-based methods. Hematoxylin and eosin (H&E) is a standard histological combination, with hematoxylin staining nuclei and eosin staining cytoplasm. Procedures typically involve fixation, sectioning, and controlled staining times, followed by mounting for examination.

Immunohistochemistry and related techniques use labeled antibodies or nucleic acid probes to localize specific molecules within tissues, providing molecularly targeted contrast. Fluorescent stains enable multi-channel imaging and quantitative analysis in research and clinical settings.

Outside biology, staining covers wood finishing, textile dyeing, and decorative coatings, where dyes or pigments color materials and may enhance durability or appearance. In materials science and metallography, staining and related colorimetric methods help reveal microstructural features or phase distributions, often in combination with etching or other preparatory steps. Safety considerations include handling hazardous dyes with appropriate ventilation, PPE, and proper waste disposal.