Colorfastness Testing - Avoiding the Nightmare!

September 20, 2010
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As all professional carpet, upholstery and – especially – rug cleaners know, color migration is the worst nightmare imaginable. Texture change? Browning? With a little effort you usually can correct those, but dye migration? That’s a whole different issue. The potential for color migration depends on the fiber, dye, dye method and cleaning method used. Obviously we aren’t talking about olefin fiber, since it always is always solution or pigment dyed. But contact-dyed wool, silk, cotton, rayon, and even nylon – well, those fibers are a concern because they will bleed, sometimes prolifically.

When you get right down to it, careful and prolonged colorfastness testing is the only way to anticipate and guard against most color migration. But even this does not provide a 100% guarantee; education, experience and professional judgment are required as well.

Although color migration can occur on carpet and upholstery as well as rugs, we’ll focus on rugs for now. The potential for color migration within a rug’s pile, or from pile yarns onto cotton or wool fringe, depends on how well dyes were applied and fixed, how well-formulated the cleaning chemical used, how much moisture was used to clean the rug, how aggressive the method of cleaning was and numerous other factors, especially the presence of urine in the rug.

Buffered cleaning products that may be suitable for synthetic fibers are the worst culprits when it comes to destabilizing the dye-fiber bond on wool, silk and even nylon rugs. Also, the wetter the rug and the longer it takes to dry, the greater the potential for bleeding or color migration.

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Since most high-value Oriental or designer rugs are made of acid-dyed wool and silk yarns, it’s very important to select and use appropriate cleaning agents. Believe me, the products you use do make a difference – a huge difference.

Recently I was demonstrating dye-bleed testing for a video I was producing for an online rug-cleaning training course. I used a WoolSafe-approved detergent with a pH of 7 on a hand-knotted rug that I knew to be a severe “bleeder.” After three hours of continuous contact with pile yarns (on the back side of the rug), I observed only slight dye transfer (photo 1).

Well, that got my curiosity up since, in the past, I had used another neutral detergent on this particular rug and it always bled – a lot! So, I located some of the non-tested, non-approved cleaner and applied it to the same rug for the same three-hour dwell time. As I suspected, the product that had not been tested caused considerable more dye migration (photo 2). Granted, both neutral detergents caused dye migration, but the bleeding from the approved product was much less severe (photo 3).

Don’t just take my word for it; go ahead and conduct your own tests. And since colorfastness testing is so critical, let me suggest three ways to perform a dye bleed test:

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The Quick or "One Minute" Test

This test typically is done while inspecting a rug before taking responsibility for cleaning it, and preferably with the customer present. Technicians should wrap a white towel around two fingers and saturate it with a mild, alkaline solution (photo 4). The saturated towel can be pressed against various colors, starting with the darkest reds, and then dark blues and even yellows.

If colors show slight bleeding in a mild alkaline solution, that doesn’t necessarily mean that the rug can’t be cleaned. It simply indicates that cleaning solutions and methods may need to be modified, acid rinses may need to be used, and extra dry vacuuming followed by rapid forced drying should take place.

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Pin-point Testing

Pin-point testing is used when small, especially dark-colored designs or patterns are used adjacent to lighter colors. The idea is to test the rug to ensure that the dark doesn’t bleed into the white portion of the rug.

The test involves saturating a cotton swab in the properly diluted solution intended for use in cleaning. Next, pile yarns are separated and the saturated swab is inserted between rows of yarns. Several swabs should be used to test all suspect colors (photo 5). Swabs should remain in the pile yarns for at least one hour, or until the solution dries. A 3X magnifying glass may be needed to inspect for slight color transfer.

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Prolonged Testing

When rugs are brought into a cleaning facility, they should be inspected carefully for any pre-existing color migration issues and other potential problems. Following vacuuming and dusting with the exception of olefin rugs they need to be dye-bleed tested.

The best way to ensure that a rug can be cleaned more aggressively (e.g., hot water extraction or submersion cleaning) without color migration either within the pile or onto fringe is with a prolonged (several hours) and preferably over night test.

In this testing procedure, three 11”x12” sheets of absorbent white paper towel folded into a 6”x11” rectangle (to form six layers) should be saturated with the properly diluted solution intended for use in cleaning the rug. The folded towel should be submersed in the cleaning solution and then, wrung out – but not completely. The towel should retain sufficient moisture to dampen rug yarns and cause migration if dyes are fugitive (photo 6).

With a few exceptions, it’s always best to test the back of a rug for color migration. That way, if color migrates slightly it will not be noticed, whereas slight color migration on the pile side of a rug might be objectionable to customers.

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Technicians should place the detergent saturated paper towel on a back-side (usually a corner) covering as many of the rug’s different colors as practical. Be sure you always test reds and all dark colors. The towel should be weighted down with a colorfast, somewhat heavy object (e.g., 2-by-4-by-8-inch or 2-by-6-by-8-inch off-white pavers weighing about four to five pounds and available at builder suppliers) to ensure complete contact between the towel and the rug. The prolonged colorfastness test should remain undisturbed for at least three hours and preferably overnight.

When a rug has a secondary backing or fabric (e.g., machine tufted, hand-tufted, hand-hooked, crewel), back-side testing is not feasible. Therefore, prolonged pile-side testing using less moisture in the towel may be the best alternative (photo 7).

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If the dyes are fugitive, there is a high likelihood that they will transfer to the towel or cotton swabs. From these tests, a trained, experienced technician can determine the appropriate and safe method for cleaning. But remember, there is always a certain level of risk involved, which should be conveyed to the customer by way of a well-worded work authorization form.

If after the cleaned rug dries completely you find that in spite of all your careful testing color has migrated from pile yarns onto the fringe, steps should be followed to correct that problem. Fringe correction will be the subject of another article; it’s not as difficult as you may think!

If you take the time to perform careful dye-bleed tests, I know you’ll sleep better and avoid the color migration nightmare!

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