It is normal for carpet color to change after it has been placed into service. Color is affected by sunlight, humidity, heat, atmospheric contaminants, cleaning chemicals, heating gases, and even foot traffic.
Some of the most common complaints with carpet color change are not really color changes at all. They are simply changes is texture or pile direction that "appear" to be a change in carpet color, but are actually related to inconsistent diffusion of light. Sounds technical, Huh? If you have reviewed our section on carpet construction, you will understand that the carpet pile leans in the direction of manufacturer. If you brush the carpet pile against the pile direction, light reflection will the altered and this area will appear darker or lighter. The whole philosophy behind "trackless" or "footprint free" carpet is to kink the yarn, so it stands straight up and helps disguise the pile lean and thus reduces the darker/lighter shade variations that causes color change and reveals foot prints. No cut pile carpet is totally "trackless" but some track less than others (Hence, the term trackless).
There are some changes in carpet color that are "unnatural", however.
Reverse Pile Direction: When carpet is installed, it must be installed in the same direction of manufacture throughout the installation. It the pile direction is reversed at a seam, one side of the seam will appear darker or lighter. This is a carpet installation defect. This is related to that diffusion of light "thing" mentioned earlier. An easy test to see if the pile has been reversed is to view the seam from one angle and one side should appear darker. Walk around to the other side of the seam and the darker side will now appear lighter.
Peaking Seams: The picture above could be a seam that peaks, if the darker/lighter color does not change when viewed from different directions. This is an extremely common occurrence and is not an installation error or manufacturing defect. When carpet is stretched taut, the seams have the tendency to rise as the carpet seam tape lines up with the carpet backing on either side of the seam. Notice the window to the right in the photo above. Light from the window could be casting a shadow on the left side of the seam creating the illusion that the left side is darker. By using overhead light (at night), you can usually discern whether the darkened left side is due to the primary light source is casting a shadow or whether there is truly a color change.
Unlevel Dye Application: Suppose you have examined all of the investigation tools mentioned above and still don't have an answer. The next logical choice is to look for manufacturing defects. There are scores of manufacturing defects that can cause a color change. The most common is unlevel dye application or "side-to-side" or "end-to-end" shading. In some cases, the production line may speed or slow and dye may be applied heavier at one end of the roll that at the other or dye may be applied heavier to the right side of the roll. This will cause a slight color change at the seams. This is rarely noticeable unless the left side of the roll is seam to the right side of the roll. In most cases, these defects are detected before leaving the plant and the goods are marked as "irregular". This "plunder" can be purchased at steep discounts through our site partners at the bottom of this page and in most cases you will never know a defect exists if the room is 12 ft wide and doesn't require a side seam. These site partners also sell first quality goods at substantial savings.
Odd Lot Yarns: Have you ever painted part of a room and switched to another can of paint of the same color to paint the rest of the room and had a color change where you changed paints? The different paint batch may have had a slight difference from batch to batch. Carpet fiber is much the same. The average carpet tufting machine uses 1100-1440 spools of yarn that spans the 12 foot width of carpet. Different yarn lots accept dye differently. If mismatched yarn lots are loaded on the same machine, there will be a noticeable color change following dyeing. Usually, when this occurs there is only one spool accidentally loaded from a different yarn lot. This forms a single thin line along the carpet length that produces a different color. Let's suppose that 20 spools from a different yarn lot were inadvertently loaded side by side on the creel. This would produce a wider, more consistent color change.
Different Dye Lot: Carpet is manufactured in dye lots and roll numbers. (definition- A quantity of carpet dyed at one time or made from yarn dyed at one time which is consistent in color throughout the fabric.) If you were to purchase two short rolls of carpet with different dye lots, it is possible to notice a color change if the two different dye lots are seamed together. Also, if the dye lots are the same, but the roll numbers are vastly different (not consecutive), there may be a slight difference in shade. This is not a manufacturing defect. The carpet retailer should check dye lots and consecutive roll number match prior to installation. I still have trouble matching socks in the morning due to this type of occurrence.
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Graeme Stephens has been running the largest owned carpet cleaning company in new Zealand for 24 years. IICRC qualified "master restoration technician"