Used in histology to differentiate collagen fibers from muscle and other tissues. Stains collagen red using picric acid and muscle fibers yellow to red depending on the formulation. Commonly applied in pathology to examine connective tissue disorders, liver fibrosis, and cardiovascular tissues. Helps visualize tissue architecture under the microscope, especially in biopsies and research studies involving tissue remodeling. Often used after fixation in formalin and processed in paraffin sections. Provides contrast that aids in identifying structural changes in tissues such as scarring or fibrosis.