Orcein solution, alcoholic with hydrochloric acid, is a staining solution for in vitro diagnostics, used especially for staining tissue samples. Its composition includes ethanol, water, orcein and hydrochloric acid. In histology and cell biology, the solution is mainly used for staining elastic fibers, collagen, nucleic acids and cellular components.

Orcein, is a natural dye mixture and has affinity for various tissue and cell structures. When combined with ethanol and water, its solubility and penetration ability is increased. Hydrochloric acid is added to enhance staining by forming an acidic medium that facilitates the binding of dye molecules to specific cell structures. This combination allows specific and optimal staining of cell and tissue samples, enabling detailed analysis and examination.