Do you guys get these approx 6x4 inch metal sheets for wall plastering in the UK ? In India they are very commonly used by painters to fill in cracks with plaster and to level out walls. They are about 1mm thick and quite cheap. Some of us use them instead of an algae scraper. They cover a larger area than most scrapers and I feel a bit safer than razor blades scratch-wise. You can even use them to clean a bit of the glass that is covered by substrate. If they rust then they are chucked since they are quite cheap and come blued so they last fairly long