The Low E coating is actually harder than the glass and consequently is quite difficult to scratch. This does not mean it cannot be scratched, as anything can be scratched if you try hard enough. However, the marks you notice might be abrasion marks. The consequence of the coating being very hard is that it can abrade other materials? So, materials rubbed across the coating can abrade and leave deposits on the surface. For example, if you rub a coin across the coating, a mark will result. The mark is caused by metal from the coin being deposited on the coating. These abrasion marks can be cleaned off and advice on how to do this can be found in the cleaning advice for Low E glass which can be found on our website.