Orceiacetic acid is an aqueous solution of the dye orcein in acetic acid. Orcein is a natural red dye extracted from lichens. In histology, orceiacetic acid is used to stain specific tissue structures, particularly connective tissue and elastic fibers, which it stains purple to brown.

Orceiacetic acid is particularly useful for visualizing elastic fibers in tissue sections because it selectively stains them. This staining allows assessment of the morphology and condition of elastic fibers in tissues, which can be important in the diagnosis of diseases such as atherosclerosis or elastofibroma.

In addition to its use in histology, orceleinacetic acid is also used in the textile industry as a dye and in microbiology to stain bacteria and fungi.