Many handicraft shoemakers use shards of broken glass as scrapers for leather and other shoe materials, especially in narrow areas or to smooth out the marks of a coarser abrasive, like a rasp.
Making
Glass scrapers can be made by scoring panes of scrap glass with the corner of a triangular file or other hard tool, then snapping along the scored line over the edge of a bench or another fixed block. The edge at the break is the edge used for scraping.