We recently had a new kitchen installed at home, included was a glass topped halogen hob. Soon after - and much to her disappointment - my mother split some sugar on the hot hob while making jam. As the manual said, the hob was allowed to cool off before cleaning; however when it came to cleaning off the hardened sugar globules they took some glass away with them, leaving a sprinkling of pits in the surface.

No abrasives were used in cleaning, just hob cleaner and a sponge, what happened?