Made in 1884 by German chemist Paul Böttiger, who first synthesized the dye while working for Bayer. Bayer rejected the dye, and so Böttiger parented it and then sold it to the rival company AGFA. Ironically, the dye ended up being so popular it almost put Bayer out of business. The dye itself has nothing to do with Congo, rather the name was chosen to capitalize off of the current interest in West Africa at the time. 

Congo Red is a carcinogen, is toxic to unborn children, and is a respiratory irritant. Goggles, gloves, protective clothing, and a mask are all recommended when handling this chemical.

Staining Procedures

Nigrosin serves as a negative stain for otherwise unstained bacteria. Nigrosin does not have any listed hazards, but reasonable caution should still be exercised. Wearing goggles and gloves is recommended. 

Staining Procedures

Rhodamine B is used as a fluorescent dye to stain myobacterium and other acid-fast species. Rhodamine B is an acute oral toxin, serious eye irritant, and potentially a carcinogen (although sources vary on this). Goggles, gloves, and protective clothing are all advised. 

Staining Procedures

Safranin O is used to stain gram negative bacteria red to contrast with a blue stain on gram positive bacteria. Safranin O is also a severe eye irritant with the potential to cause permanent eye damage. Gloves, goggles, and protective clothing are all advised, with an emphasis on the use of goggles. 

Staining Procedures