Color Fastness Test Calculator

Color fastness isn't one number — this calculator tracks three separate fastness ratings (1-5, where 5 means no visible change) because a dye can behave very differently under different kinds of stress: wash fastness (resistance to color loss in the laundry), light fastness (resistance to UV-driven fading), and rub fastness or "crocking" (resistance to color transferring off through friction). Wash and rub fastness follow the ISO 105 Grey Scale directly, while light fastness starts from the Blue Wool Scale — a distinct standard normally scored 1-8 — rescaled onto the same 1-5 range so all three sit on one comparable axis. Each starts from a base rating tied to the dye class you select — reactive dyes on cotton and disperse dyes on polyester both start strong, while direct dyes and natural dyes start noticeably weaker — and each is then degraded by the conditions you enter: wash fastness drops with water temperature above 30°C and with bleach exposure (chlorine bleach penalizes far more heavily than oxygen bleach), light fastness drops with weekly sun exposure hours, and all three degrade logarithmically with cumulative wash cycles, reflecting that most cumulative fading happens across a garment's early wash life before tapering off.

An overall color-retention percentage is derived by averaging the three current fastness scores and scaling to 100, and a bleeding-risk score flags garments likely to transfer dye onto other items in the wash, which rises both as fastness falls and when the wash temperature exceeds that dye class's recommended maximum. Because the model works from typical dye-class behavior rather than a lab test of your specific garment, actual results can vary with dye lot, mordanting, and finishing treatments — treat these figures as a rough forecast, not a stand-in for physically testing a hidden seam of the real garment.