Silicone caulk, used for sealing around areas such as sinks and bathtubs, attaches quickly to surfaces. When silicone caulk bonds to window glass and hardens, removing it proves to be a challenge. The hard caulk has a cementlike quality that requires heat to soften the substance enough to extract it from the window without scratching the glass. With a sharp razor and heat you can remove silicone marks from windows.
Place the nozzle of a hair dryer 1 inch from the silicone caulk on the window. Set the hair dryer to hot and heat the caulk for 30 seconds to one minute.
Place the edge of a razor blade at one end of the caulk and slowly edge it under. Keep the razor flush with the window to avoid scratching the glass. The heat causes the caulk to become brittle so tiny pieces may crumble from the glass.
Wipe the loose caulking from the window with a clean rag. Heat the remaining caulk again with the blow dryer. Continue chipping away at the caulk with the razor and heating it with the hair dryer until only small fragments remain.
Wet a clean rag with 1 to 2 tsp white spirit. Rub the white spirit into the tiny remaining pieces of caulk on the window glass. The white spirit help loosen and dislodge the rest of the silicone caulk.
Remove the white spirit from the window with a sponge dipped into a sink of warm water and 1 tsp mild dish soap. After cleaning, rinse the soap suds from the window with a wet sponge, then dry with a lint-free cloth.
Wear thick work gloves when using the razor blade to avoid cuts.