Ammonium oxalate crystal violet staining solution (1%) is a component of Gram staining method, mainly composed of ammonium oxalate, 1% crystal violet, ethanol, etc. It is commonly used in the differential staining of Gram bacteria.

Gram-positive bacteria staining in the cell by ammonium oxalate crystal violet staining and then Gram iodine solution treatment, the formation of insoluble complex, the complex can not pass through the cell wall, not easy to be decolorized by ethanol, so maintain the purple color, stained bacteria and the environment to form a stark contrast, the bacterial form, arrangement and certain structural features can be clearly observed, but also through the choice of red re-staining with sandy yellow or litharic carbonate, can be distinguished between Gram-positive and negative bacteria.