What do Carpet Cleaners Need to Know About Dye Stains?

By Jim Smith

To learn what knowledge is necessary for carpet cleaners when it comes to dye stains, first, we need to define what a stain is. According to cleaning standards, stains are foreign and unwanted substances that are not removed with cleaning. Aside from dyes, foods and oils make stains as well.  

However, dye stains are generally more challenging. In addition, dye stains can chemically react with some fibers. If the dye has not chemically reacted, then it will have a physical bond due to a propensity for chemical reactions.    

Understanding the physical bond    

Physical bonds and chemical reactions come from propensities of substances to either add or remove protons, electrons, or both. Proton propensities are measured with pH meters. Most know that their values are generally from zero to 14, with seven being neutral. Thus, if an acid does not react with something that is cationic, then it will have a physical bond that constitutes a stain.    

Electrons are measured with an Oxidization Reduction Propensity (ORP) meter which is like a voltmeter. Their values are in millivolts or ‘mv.’ What is not widely known is that negative values are generally reducers while positive ones are oxidizers. Both reducers and oxidizers are considered bleaches. In other words, ORP meters can measure the strength of a certain bleach.  

It is important to remember that when using pH and ORP meters, one should use meters that are designed for textiles. This type of meter will have a flat surface which will yield a reading when placed on a moist fiber.    

Reducing bleaches work best on acid-dyes which are common to many synthetic colorants, especially red. Oxidizers generally work best on food and beverage-related dyes, especially blue. In addition, they work on dyes found in dry solvents, such as wood stains and makeup.  

Using reducers  effectively  

Dye stains that yield values between three to six are generally acid-dye stains or come from things like coffee and tea. A substance called sodium bisulfite is generally effective in destroying coffee and tea specifically. Sodium bisulfite has a pH of 5.5 and an ORP of negative 195 mv. This is essentially what most coffee, tea, and browning solutions are.    

Reducers are made more powerful with heat which is needed on synthetic dye stains. They frequently have ORP values between negative 850 to negative 460. Reducing bleaches lose potency with time which is a primary reason why many fail to remove certain stains. One should always check these products with their ORP meters to make sure they are still effective.    

The most common way of using a strong reducer is with the heat transfer method. This involves wetting the stain with the product followed by placing a wet terry towel over it, then laying a hot steam iron on top of the towel for about 40 seconds. This application frequently requires repeating. The dye that wicks into the towel had a physical bond with the fiber. If the stain simply disappears, it was due to reduction. Stains like these frequently occur on nylon and wool.  

This is because nylon is cationic. Cationic is related to alkalinity, except the fiber is insoluble. In other words, a cationic is like an alkaline absorbent that can physically bond or can chemically react with aqueous acids such as acid-dyes.  

Wool, on the other hand, is naturally anionic, but frequently has an acid film yielding a pH of 5.5 or as low as 2.5. This reverses wool’s polarity making it cationic. Thus, removing dye stains on wool may take a supplementary product or a different product made for wool.    

Working with oxidizers    

Mild oxidizers such as 3% hydrogen peroxide, pH 5.5; ORP 360 mv are also effective in removing coffee, tea, and cellulosic browning. However, it will destroy other stains like mustard, blood, and urine likewise.  

Stronger oxidizers will have ORP values from 460 to 850 mv. These oxidizers are made stronger with ultraviolet light at 365 nm. They would be effective in removing hair dye, soft drinks, dye stains from food, black dye from artificially colored coffee and tea, blue dye from toilet bowl cleaners, and furniture stains.    

Summarizing dye stain removal methods  

All in all, the takeaway  of this article and the valuable information presented is that dye stains can be removed, but it requires training as well as the use of powerful spotters which are made especially for carpet.  

Considering the fact that success can be greatly improved with a deeper understanding of chemistry and the use of pH and ORP meters, I hope you take this knowledge, train your team accordingly, and see the success that proper dye stain removal training can bring.