Things You'll Need
Sticky tape residue on windowsills attracts more dirt if it's not cleaned off properly. The residue also eventually hardens, especially in sunny windows where the sill becomes warm during the day. Both regular tape and the double-sided tape used for winter weatherization plastics leave behind a similar adhesive after removal. Cleaning it off as soon as you remove the tape prevents permanent stains or damage. Metal or aluminum sills are less prone to damage than wood ones, but you can remove the tape successfully regardless of the sill material.
Peel the tape from the windowsill. Insert the tip of a plastic knife under the tape to lift it, if necessary. Peel the tape off slowly on painted wood sills so it doesn't lift the paint.
Rub your thumb over the tape residue so it balls up. Remove as much residue as you can with this method.
Moisten a cleaning rag with rubbing alcohol. Rub the tape with the alcohol soaked cloth, rewetting it as necessary, until the tape residue is completely removed.
Combine a tablespoon of mild liquid dish detergent with 1 quart of warm water. Wet a cleaning rag in the soapy water.
Wash the entire windowsill with the soapy water. Rinse with clear water then wipe with a dry cloth.
Water can cause the residue to adhere more fully or spread it around. Only wash with water after all residue is removed.
Test the alcohol on the underside of the sill or in another hidden area first to make sure it doesn't damage the finish.