What you were experiencing is a phenomenon known as Heightened Awareness Syndrome or H.A.S. for short. The carpet has come under unusual scrutiny because something has been done to it. You were the last one to touch the carpet, and you will now get the blame for anything that your contact feels is not perfectly acceptable.
Anything you fail to bring to your customer’s attention prior to cleaning the carpet will most certainly be brought to your attention afterwards. Unfortunately, even technically correct explanations of what occurred to the carpet only resonate in some peoples’ ears as an excuse.
Three common, but very different concerns, I see quite often in commercial settings can be diagnosed and easily explained to your customer prior to the cleaning. These are the phenomenon known as shading, lighting, and shadows.
Shading, primarily observed in cut pile carpet and often in loop pile carpet, occurs when yarns bend in different directions from surrounding yarns. Shading can be observed when vacuuming or cleaning and the yarns take on different shades of color as they flex back and forth. Shading is the phenomenon you are looking at when there is a dark spot on the carpet viewed from one direction and a light spot viewed from the opposite direction. The strange thing is that I have seen this phenomenon occur to carpet that has never been put into daily use.
As a conscientious crew manager or cleaner, you may be inclined to tell the customer that these dark/light spots can be solved in the offices or corridors. Save your breath and energy, because no matter how much scrubbing, brushing or steaming you do, you will be chagrined to discover that the color difference is still there when the carpet is dry. You may have been able to make it look better, but it will not go away.
In daylight, the carpet in an office or lunchroom with windows appears medium-brown. However, under incandescent lighting at night, the carpet has turned to a golden yellow-brown color. Or, it can become a dark, cold-brown color under fluorescent lighting. Walking through the building with your contact before the cleaning gives you the chance to point out that the carpet in the hallway appears darker than the carpet in the windowed room, which may save you from receiving a callback later.
Another thing to watch out for is recessed lighting. I have two photos I bring out whenever I talk about lighting. The first one clearly shows a bathroom entryway next to a janitor’s closet door and a yellow caution placard. A bleached-out spot is clearly visible where some chemicals were spilled. The second photo shows the same bathroom, closet door and placard. Another photo, taken several feet away, clearly shows how a recessed light above the “bleach” spot makes the carpet directly under it appear lighter than the rest of the carpet.
In commercial buildings, many different types of light and countless types of light fixtures can be found. Be on the lookout for the infamous lurking shadow these light sources can cause.
For more information related to shading, watermarking and pooling, see the Institute of Inspection Cleaning and Restoration Certification (IICRC) Reference Guide for Inspection of Textile Floorcoverings or the IICRC SOO1 Carpet Cleaning Standard.