Frequently Asked Questions
Q: What colorfastness rating should I expect on black and navy knitted garments?
A: Black and navy are the hardest shades to achieve high fastness on. A well-dyed black cotton knit should achieve wash fastness of 4–4.5 and rub fastness of 3.5–4. Anything below 3.5 on rub fastness for dark shades is commercially problematic — it will transfer visibly to light fabrics, especially when wet. Ask your supplier for lab certificates specifically on your darkest shades.
Q: Does repeated washing degrade colorfastness over time?
A: Yes, gradually. Even a 4.5-rated fabric will shift toward 4 after 20–30 washes, and toward 3.5 after 50+. The rate depends on wash temperature, detergent harshness, and whether the garment is tumble-dried. Higher initial fastness ratings buy more usable wash cycles before noticeable fading. For hospitality linen that sees 100+ washes, specify 4.5–5 ratings at the outset.
Q: What is the difference between reactive and vat dyes for colorfastness?
A: Reactive dyes bond chemically with cotton fibres — they’re the standard for bright, saturated colours with good wash fastness (4–4.5). Vat dyes have the highest wash and light fastness (4.5–5) and are preferred for workwear, hospitality linen, and anything requiring very long service life. Vat dyes cost more and require more complex processing, but they’re worth it for demanding applications.
Q: Can I specify a minimum colorfastness rating in my purchase order?
A: Absolutely — and you should. Standard wording: “Wash fastness ISO 105-C06 minimum Grade 4; Rub fastness ISO 105-X12 minimum Grade 3.5 (wet), Grade 4 (dry).” Include this in your tech pack or purchase order terms. Reputable manufacturers like Al Madni will confirm compliance and provide test certificates with the shipment.
Q: How long does light fastness testing take, and when should I request it?
A: Light fastness testing (ISO 105-B02) takes 24–72 hours depending on the required exposure level. Request it if your product will be displayed in bright retail environments, used outdoors, or stored for extended periods before sale. It’s less commonly tested for basic garments, but essential for outdoor textiles, upholstery, and sun-exposed home textile items.
Q: Is there anything a buyer can do to preserve colorfastness after purchase?
A: Yes. Washing inside-out reduces surface abrasion. Cold water (30°C max) causes less dye migration than hot. Colour-safe detergents without bleaching agents protect reactive dye bonds. Avoid prolonged soaking in water. Line-dry away from direct sunlight. These care steps extend the useful life of any garment’s colour, regardless of initial fastness rating.