Gutter brightening is when after cleaning the organic matter (mold, mildew, algae & dirt) off the gutter, your gutter still looks dingy. To get that cleaned, you have to do a process called gutter brightening or whitening. You use a special chemical (Gutter Grenade) that is used to take away the oxidation that has accumulated over many years. This can only be done if your gutters are in overall good shape paint wise. We spray the chemical on, scrub with soft brush, then rinse with clean water.