Formalin 4 %, carbonate buffer, pH neutral (green) is an in vitro diagnostic agent used in histological, histopathological and cytological diagnostics. The main component, formaldehyde, interacts with proteins in tissue samples, causing cross-linking and thus fixing and preserving tissue structure. Calcium carbonate serves as a buffer, ensuring a neutral pH to ensure optimal morphology and antigen preservation. The green coloration by light green yellowish allows easy visual identification. Once applied, the product provides high quality preservation of tissue samples for microscopic examination and diagnosis. With a molarity and osmolarity of 1.33 mol/L and 1.33 osmol/L, respectively, for the formalin and a buffer capacity of 0.1 mol/L for the calcium carbonate, this product provides a reliable and effective solution for tissue preservation.