Capillary Wicking Distance & Time in Knit Structures

Washburn assumes a single equivalent cylindrical capillary, a Newtonian fluid, no evaporation and no gravity — every one of which is wrong for blood on clothing. Blood is a shear-thinning suspension that clots as it spreads, so its effective viscosity rises with time rather than staying constant; it evaporates and absorbs into fibres as well as travelling between them; and the effective capillary radius of a real knit is a fitted quantity, not a measurable one. **Time-since-deposition cannot be reliably inferred from stain size**, and this tool must not be used that way. It illustrates the physics of directional wicking and the square-root relationship. Forensic conclusions require validated methods, controlled comparison materials and a qualified examiner.