How many times have you wished you could look into the future when it comes to cleaning certain things?

Having been in the business for over 40 years, my motto has become, “It is not how much you make; it’s how much you get to keep.” In other words, I would have chosen not to clean some carpet and pieces of upholstery if I had known their hidden problems.

The electronic pH pen has become a time machine that allows cleaners to see potential disasters. Here are several things to watch out for:

Rated R: Under three (pH) not advised

Do not clean upholstery that has a pH below 3. This is normally an indication of a deteriorating flame retardant.

This flame retardant originates from the ticking (inside the cover) rather than from the face fabric. However, it wicks into the cover and turns undyed cotton either yellow or brown. Dyed fabrics frequently turn red because of indicator dyes.

In theory, this problem can be addressed by rinsing the fabric over and over again with baking soda, sodium bicarbonate, but many have found that this is not cost effective.

A multi-colored nylon carpet with a pH below 3 is an indication of a cross-dyed system and a potential bleeder. Cross dying is done in a beck system.

One needs to understand that nylon’s normal polarity is cationic, meaning it is like an alkaline. Cationic fibers are usually dyed with acid dyes. However, nylon can be considered to be amphoteric. This means that under certain conditions, its polarity can be reversed to become anionic. In cross dying, carpet with anionic and cationic fibers are dyed with two different kinds dyes that have two different colors. This yields multi-colored faceyarn with a pH under 3.

The problem is when the acidity applied by manufacturing is counteracted by alkalinity from cleaning, the carpet bleeds. If the pH can be maintained, then carpet can be cleaned. But there is no way to practically know this except from a pH meter reading.

What about wool?

Chemically, wool is similar to nylon in several ways. It too can be considered amphoteric; however, wool’s polarity is anionic (acid like); but it commonly is dyed with acid dyes. One should ask why and how an acid fiber can be dyed with an acid dye.

The answer to the “why” question is: If wool was dyed with a base dye, the pH of the dye bath would need to be raised to a point where its cuticles would be removed. Degrading wool with alkalinity is called felting.

The answer to the “how” question is that wool typically is dyed in baths between a pH of 2.5 and 5.5. This low-pH dye bath reverses wool’s polarity to cationic. It is common to get a pH values of 5.5 or lower before cleaning wool. Field experience has shown most wool carpet starts to lose blue dye, when pH values go over 5.9.

There are times when wool or especially wool/rayon (viscose) blends have not been dyed; yet, they still have color due to the natural hues of wool. It is common for carpet manufacturers of this kind of product to specify either dry foam or dry compound methods of cleaning because their textiles are not colorfast. The pH readings of undyed wools will be common for that of soil at a pH of 6.1 to 6.7.

The unsuspecting cleaners could be responsible for a bleeder with undyed wools. “How can that happen?” you ask. Read and understand the S100 (sixth edition), which says:

4.1.1 Fibers

When end users purchase carpet, they should be aware of fiber characteristics that affect long-term performance. The amount of traffic, soiling conditions, and the type and frequency of spots or stains should all be considered when selecting carpet.

Likewise, cleaners should be aware of fiber characteristics that can affect cleaning outcome and communicate with end users to create realistic expectations of cleaning.

Colorfastness is an important characteristic of the fiber. There are only three options on how to know if a wool carpet is colorfast or suitable for wet cleaning methods. Either read the manufacturer’s cleaning specifications, or do a colorfast test, or take a simple pH reading before cleaning. The standard means the unsuspected cleaner could be liable for the bleeding even when wool approved for cleaning products is used.


Electronic pH meters have become a fundamental tool for professional cleaners. Get one and use it. It’s worth the investment.

James (Jim) B. Smith is an IICRC-approved instructor and a senior practicing inspector and part of the voting consensus of the IICRC S100 cleaning standard. His educational studies come from Texas A&M University and the University of Houston. He has been in the cleaning industry since 1975. For more information, visit his website at or call (972) 334-0533 or (800) 675-4003.

More articles from Jim Smith:

Applications of Absorption

This article shows that by probing deeper into absorption, we can achieve great results when cleaning carpet.

The Resoiling Dilemma

The information in this article presents a new theoretical approach to understanding detergency and resoiling, based upon the topics of “polarities” and “states of matter.”