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Buffering Blame

May 4, 2009
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Dye migration on hand-knotted rug


Rugs, carpet; if they’re made of wool, what’s the difference? They both require the very best cleaner that money can buy – well, that money can hire.

Problem is, most carpet cleaners – even the good ones – clean mostly synthetic carpet in their day-to-day operation. Good old durable, color-fast nylon, polyester or olefin, using a good old high-pH (about a gazillion!) traffic lane cleaner that’ll take the hide off a water buffalo.

“So what’s the problem?” you ask.

Well, consider this: if you remember what you learned in that course you took many years ago, when the dyeing process takes place, acid dyes react with the wool fiber and the dye and the fiber become attached to one another at a molecular level. It’s a bit like a magnet whose opposite ends are attracted to each other. That’s a bit oversimplified, but you get the idea.

In this way the dye is transferred from the dye bath to the wool fiber. Because the dye needs a positive charge, the reaction is carried out under acid conditions. The finished carpet, therefore, is acidic in pH, and if it’s wool, often in a range of pH 4-5, but sometimes as low as pH 2.5 and as high as pH 6.5, depending on the dyeing process.

Carpet-cleaning technicians who understand this have all the information necessary to clean a wool carpet without the risk of color bleeding or dye migration.

So what causes dye bleeding to occur on wool carpet or rugs?

Bleeding starts when the dye-fiber bond is destabilized. Clearly, it can be destabilized by raising pH, which affects the positive and negative charges of the dye and fiber respectively.

Consider the following scenario: A wool carpet with dark-red and white colors has a pH of 4, and the dye-fiber bond is stable up to a pH of 6. The carpet is then cleaned by your competitor using a cleaning chemical at a pH of 9. This can cause the pH of the carpet to increase, or become more alkaline.

At first, the carpet’s pH may only move to 5, and the dye-fiber bond continues to remain stable. A year later, that same competitor cleans the same carpet again, using the same alkaline cleaner considered safe on nylon. The pH drifts farther towards the alkaline side.

Eventually, the carpet needs to be cleaned again and the customer decides to give your firm a try. You have some training – maybe one or two IICRC certifications – so you precondition the carpet with a pH of 7 and even follow up with an acid rinse (pH 3). But because the cleaning product the competitor used was buffered (read: “stabilized”), the pH of the fiber remains alkaline. More alkaline, in fact, than the dye-fiber bond is able to tolerate.

Wool carpet before dye migration

So what happens? Well, initially the dark red starts to bleed into the white as the color becomes increasingly unstable. Eventually, other colors become destabilized and…well, you get the picture and it isn’t very pretty.

So whose fault is it? Your competitor’s, of course.

Who gets the blame? Congratulations! How’s that funny-colored carpet or rug going to look in your living room?

The situation is made more complicated by the fact that there are some cleaning chemicals with a pH of 9 or more that will not cause bleeding, while there are some of perhaps only pH 8 that will. This means that simply choosing a chemical on the basis of pH alone just isn’t good enough.

The explanation for this fiasco is really quite simple. A carpet-cleaning product is a mixture of chemicals blended by the manufacturer to give certain performance characteristics. One of the cleaning chemical ingredients, known as a buffer, has the effect of stabilizing the pH of the mixture so that, even with an acid rinse, it won’t change – at least not much.

Consider a carpet-cleaning product for stain-resistant nylon that has been buffered at a pH of 10. Using this product on wool carpet at pH 4 can cause the carpet pH to drift upwards and become more alkaline.

Now, consider an un-buffered product with a pH of 10. When used to clean wool carpet, the cleaning product’s pH may actually drift downward, because the carpet is more highly buffered after dyeing than is the cleaning product. This product is much less likely to cause bleeding than the one in the first example. Sounds strange, doesn’t it?

Wool carpet after dye migration

If an untrained cleaning technician uses a buffered alkaline cleaner on wool carpet, as in the scenario above, it may not bleed with the first cleaning. Later, you clean the carpet with an approved cleaner – even using an acid rinse – and the carpet dye bleeds because buffering stabilizes the alkaline pH of the previous (and improper) detergent. Again, the other cleaning technician caused the problem, but you get the blame! That’s why careful pre-inspection, including cleaning history and pH testing, is important, and especially so when cleaning expensive wool carpet or rugs.

So how do you tell if a product has been buffered? That’s the million-dollar question. Start first by asking your supplier. When you get the “deer in the headlights” stare from him or her, that’s when they should ask the chemical manufacturer.

Can you field test for buffering? Probably not accurately. But you can get an approximate idea of the carpet’s pH.

pH paper or meters that are practical for field use and are affordable and easy to use. A meter can be a powerful sales tool when used by professional cleaning technicians to test wool carpet before cleaning. Today’s models even fit into shirt pockets. A meter with a flat surface is necessary to obtain readings on carpet and upholstery fabrics.

Before the pH of the carpet can be measured, the pile has to be moistened. This is best done with a trigger sprayer with distilled water. Tap water is not recommended since, in some geographical areas, it may affect pH readings.

The bottom line is, any product used to clean wool carpet should be one that is specifically tested and approved by a credible organization for use on wool. More than 140 products have been tested and approved for uses on wool by WoolSafe, possibly one of yours. It’s worth checking out: the carpet (or rug) you save could be your customer’s!

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