Colour Fastness to Rain and Water Drop Testing
topic
Colour fastness to rain (ISO 105-E09), water spotting (AATCC TM104), and water drop (ISO 105-E07) evaluates the resistance of dyed and printed textiles to colour change and mark formation from localised water contact — relevant for rainwear, outdoor upholstery, and water-repellent treated fabrics where water-spot marks are a consumer quality complaint even when overall waterproofness is adequate. ISO 105-E09 (rain fastness, SDL Atlas Rain Tester): specimen mounted on inclined board (45°), simulated rain drops (distilled water, 0.1 mL drop size, 500 drops/min, 3 minutes exposure), specimen assessed against dry unexposed control — water-spot marks caused by selective dye removal at water drop impact point (surfing wave of concentrated dye migrating to drop edge during drying — coffee-ring effect). ISO 105-E07 (water drop method): single 0.05 mL distilled water drop applied to specimen surface, allowed to evaporate naturally, ring mark assessed on grey scale — highly sensitive to hydrophilic dyes with high surface mobility. AATCC TM104 (water spotting, 1 mL drop on inclined fabric, rated 1–5 against photographic standard after drying): grade 5 = no mark, grade 1 = severe ring mark — specification for rainwear outer shell ≥ grade 4. DWR (durable water repellent) finish effect on water spotting: wax-finished or DWR-treated fabric grade 4–5 (water beads off, dye not mobilised); unwaxed cotton grade 2–3 (water absorbed, dye migrates to drop ring during evaporation). Print water spotting (pigment versus reactive print): pigment-printed fabric grade 4–5 (pigment fixed in resin binder, water-insoluble); reactive-printed fabric grade 3–4 if properly washed-off; poorly washed-off reactive print grade 1–2 (hydrolysed reactive dye highly mobile in water drop — severe ring staining on drying).
Role
Rain and water drop fastness testing reveals the localised dye mobility that fabric-immersion tests cannot detect — water spotting failure on expensive fashion rainwear generates immediate consumer complaints visible after single rain exposure, making water drop fastness testing the critical quality check for all DWR-treated and rain-resistant outer shell fabrics before retail distribution.