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How to clean windows
Clean stubborn stains.
Outside windows are especially prone to stubborn stains because they are exposed to hard water runoff, minerals, bird droppings, and elements that can cake on dirt and grime. There are a few methods you can try to remove marks on inside or outside windows :
Use a mineral deposit removing cleaner, such as clr.
Dampen a sponge with cleaner and rub at the stains on the windows. Rinse the area with water and proceed with regular cleaning.