Typically a window cleaning approved razor is used to remove these substances, and a certain method to perform the removal is needed. 0000 Steel wool (the finest) also works well to remove mineral stains, though again, extra precautions should be used to remove materials with abrasives which is done with a certain method. Tempered glass must be handled with extreme caution, as it is made by a different manufacturing process than regular glass, and is more prone to damage done by abrasives. When used correctly however, these tools are effective and damage is minimal to none. Removing these materials does take time and patience and could be more expensive to clean, depending on amount on windows and scope of deposits.