‘Dyeing’ to Understand Color: How pH Levels Affect Rug Cleaning


By Dr. Ágnes Zsednai

One of the main characteristics of a carpet is its color. Fashion changes all the time Äì nowadays, in the average household, carpets are mainly beige and grey; gone are the lively colors and vivid patterns of the 1950’s Axminsters.


But this isn’t the case when it comes to most modern rugs which still don all the colors of the rainbow in storesÄì but will they really retain those vibrant color pops even after cleaning?


Not causing the colors to bleed is one of the main worries of many professional cleaners, and thus, it is the topic of many training courses and trade articles.

Wool Dyeing Basics

We all know that wool is dyed under acid conditions with a range of acid dyes. These negatively charged dyes attach themselves to—and penetrate—the positively charged wool fiber at low (sometimes very low) pH.levels.

Having said this, you disturb that low pH at your own peril: as in doing so, you might end up with the dreaded color bleed you hope to never experience.

Controlling What we can

Dyeing, as well as the subsequent cleaning of rugs, employs complicated chemistry. But the important factors can be demonstrated in simple experiments. In this article, we concentrate on what we know and can control, namely the pH of the liquid we hit the colored yarn with. All experiments were done at room temperature, using distilled water and pure chemicals. While the age of the wool was not determined during the process, the pH results should help showcase how wool age is hardly as important as pH balance is during the cleaning process.


During this experiment, we collected 16 different colored samples from four wool-rich carpets, measured their pH, and attempted to change it to make the dyes run. As expected, all the wool yarns had an acidic pH, which is the result of the dying process. Again, for the sake of standardizing what we could, we used tufts from wool carpets, not handmade rugs. These samples were dyed with synthetic dyes, not less-stable vegetable ones, so they should have been more resistant to chemistry. The goal of avoiding vegetable dyes and mordants was to showcase how even the most resistant dyes can bleed with the wrong chemistry. None of the samples showed any bleeding in water alone.


First, we investigated what happened if we raised the pH of the distilled water containing the tufts by adding the same amount of sodium hydroxide (NaOH) to each sample. The starting pH of the yarns ranged from 3.5 to 5.9; the end pH of the same yarns ranged from 10.6 to 11.7. see table 1.

Table 1: Yarn samples and their pH

Code Yarn Colour Carpet pH after 20 mins pH with 0.5 ml 0.1 N NaOH àÜpH Bleeding
8 Pink Purple woven 3.45 11.52 8.07 +++
7 Light Purple Purple woven 3.51 11.67 8.16 +++
9 White Purple woven 3.59 11.51 7.92 N/A
13 Dark Green Multi-stripe tufted 3.59 10.56 6.97 +++
3 White Grey Woven 3.68 11.09 7.41 N/A
4 Blue Grey Woven 3.99 11.14 7.15 +++
2 Dark Grey Grey Woven 4.31 11.07 6.76 +++
1 Light Grey Grey Woven 4.45 11.12 6.67 ++
5 Dark Purple Purple woven 4.69 11.45 6.76 ++
6 Medium Purple Purple woven 5.10 11.56 6.46 +
12 Light Green Multi-stripe tufted 5.17 11.52 6.35
11 Beige Multi-stripe tufted 5.23 11.37 6.14
16 Green Single color tufted 5.44 11.05 5.61 +
10 Red Multi-stripe tufted 5.53 11.50 5.97
14 Brown Multi-stripe tufted 5.76 11.49 5.73
17 Distilled Water N/A 5.82 11.50 5.68 N/A
15 Orange Multi-stripe tufted 5.92 11.37 5.45

An interesting observation is the range of the original pH within the patterned carpets according to indivi

Cleanfax Staff

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