It depends. Berryman offers two different products under the Chem-Dip name. Part #0905 is a 5-gallon product that is very aggressive towards many types of plastic, rubber, and paint but is completely safe for extended soak times with all metals. Part #0996 comes in a 1-gallon paint can that is completely safe on the vast majority of plastics, rubber, and paint, as well as most metals. However, some aluminum and aluminum alloys are susceptible to discoloration, so we recommend limiting your soak time to 30-minute intervals with a maximum of about 4 hours. If your part is aluminum and you soaked it in 0996 overnight, it may have darkened. Generally, the affect is only cosmetic, though.