Papanicolaou stain
Papanicolaou stain (also Papanicolaou's stain and Pap stain) is a multichromatic (multicolored) cytological staining technique developed by George Papanicolaou in 1942. The Papanicolaou stain is one of the most widely used stains in cytology, where it is used to aid pathologists in making a diagnosis. Although most notable for its use in the detection of cervical cancer in the Pap test or Pap smear, it is also used to stain non-gynecological specimen preparations from a variety of bodily secretions and from small needle biopsies of organs and tissues. Papanicolaou published three formulations of this stain in  1942, 1954, and 1960. Usage. Pap staining is used to differentiate cells in smear preparations (in which samples are spread or smeared onto a glass microscope slide) from various bodily secretions and needle biopsies; the specimens may include gynecological smears (Pap smears), sputum, brushings, washings, urine, cerebrospinal fluid, abdominal fluid, pleural fluid, synovial fluid, seminal fluid, fine needle aspirations, tumor touch samples, or other materials containing loose cells. The pap stain is not fully standardized and comes in several formulations, differing in the exact dyes used, their ratios, and timing of the process. Pap staining is usually associated with cytopathology  in which loose cells are examined, but the stain has also been modified and used on tissue slices. Pap test. Pap staining is used in the Pap smear (or Pap test) and is a reliable technique in cervical cancer screening in gynecology. Generalized staining method. The classic form of the Papanicolaou stain involves five stains in three solutions. The counterstains are dissolved in 95% ethyl alcohol which prevents cells from over staining which would obscure nuclear detail and cell outlines especially in the case when cells are overlapping on the slide. Phosphotungstic acid is added to adjust the pH of  counterstains and helps to optimize the color intensity. The EA counterstain contains Bismarck brown and phosphotungstic acid, which when in combination, cause both to precipitate out of solution, reducing the useful life of the mixture. Results. The stain should result in cells that are fairly transparent so even thicker specimens with overlapping cells can be interpreted. Cell nuclei should be crisp, blue to black on color and the chromatin patterns of the nucleus should be well defined. Cell cytoplasm stains blue-green and keratin stains orange in color. Eosin Y stains the superficial epithelial squamous cells, nucleoli, cilia, and red  blood cells. Light Green SF yellowish stains the cytoplasm of other cells, other than superficial squamous cells. Superficial cells are orange to pink, and intermediate and parabasal cells are turquoise green to blue. Ultrafast Papanicolaou stain. Ultrafast Papanicolaou stain is an alternative for the fine needle aspiration samples, developed to achieve comparable visual clarity in significantly shorter time. The process differs in rehydration of the air-dried smear with saline, use 4% formaldehyde in 65% ethanol fixative, and use of Richard-Allan Hematoxylin-2 and Cyto-Stain, resulting in a 90-second process yielding transparent polychromatic stains.