Every so often, we'll have a job where we see gray shading around the baseboards of a room. This typically happens on the upper floors of a house around exterior walls (or under doors). As with everything we encounter, we use all our expertise and every potential cleaning agent to make the carpet look as good as possible. Sometimes, we can remove it completely, and other times we can lighten it, but unfortunately this "filter shading" is often permanent.

Why does this happen? "Filter shading" occurs when a house's HVAC air filters stop removing the microscopic carbon-based particulates in the air. Because houses aren't perfectly sealed, air flows through the seams where floor and wall meet, more so on the upper floors. As air, rich in microscopic carbon is pulled through the seam, carpet along the baseboard acts as a de-facto air filter and traps those particles. Their microscopic size allows them to get deep into the fibers, and since carbon is insoluble, it doesn't respond to steam cleaning. Our thorough approach will remove any water soluble (non-carbon) elements, and we will also apply reducing agents to try and alter the chemical structure of the shading so it doesn't show as much. Most of the time, however, that gray shading is permanent.

So, the best way to deal with filter shading is to prevent it before it occurs, and the following steps will help immeasurably:

• Replace your air filters regularly so they do their job pulling particulates out of the air
• Vacuum around baseboards often
• Smoking contributes to the fleet of airborne particulates, so smoke outside whenever you can