Your Cleaning Made My Carpet Turn Violet!.

This comment could ruin your day if a customer calls with a message like that!

This is a true story about a cleaner who found extensive rust on a commercial carpet cleaning job where a metal cabinet had been placed. He applied a rust remover to the stained area, and the rust disappeared quickly. 
The carpet cleaned well afterward, but when dry, the areas that were treated with the rust remover had turned violet!

 "This carpet turned violet where rust remover was applied!” 

 What Happened to Cause This Reaction?

The strong acid products that professionals use for rust removal are usually safe to apply to carpets, but not always. Some carpet dyes react when very low pH or very high pH products are used on them, and the chemical reaction can cause dramatic color changes. 

The best way to understand this problem would be to compare it to the use of  pH paper, since pH paper is treated with special dyes that react with the products you are testing, and it lets you know what the pH of the material is that you are testing.

However, when this happens on something you are cleaning, it can be both frustrating and frightening!

The solution to this problem is to treat the stained area with the opposite pH to reverse the color change. In this case, even though the cleaner applied a traffic lane pre-spray that was alkaline after he treated the rust, its pH wasn't as high as needed to prevent the problem.

To correct the problem, ammonia was needed, as it has a pH of 11.6, which is far higher than the pH of the traffic lane pre-spray he applied (9.5)

The application of ammonia reversed the pH reaction and brought the carpet back to its original color.

"The application of ammonia neutralized the acidic condition that caused the violet discoloration of the carpet”

How Could This Have Been Prevented?

NOTE: The cleaner did NOTHING wrong. The cleaner followed the label directions, which said “extract with clear water or cleaning solution”, which is what he did.

However, there are also directions on most rust removers to pretest for colorfastness, which is often overlooked.

However, in this case, it might have been wise!

SUMMARY COMMENT:

If you're asked to use a rust remover over a very large area, as was the case here, it would be wise to treat and clean a small area first. Had that been done, the problem could have been seen, corrected, and then the cleaning company owner could have decided if treating the entire area was wise or not, or had the customer assume some responsibility.